_Genus_--SCALPELLUM. Pls. V, VI.
SCALPELLUM. _Leach._ Journ. de Physique, t. lx.x.xv, July, 1817.
LEPAS. _Linn._ Systema Naturae, 1767.
POLLICIPES. _Lamarck._ Animaux sans Vertebres, 1818.
POLYLEPAS. _De Blainville._ Dict. des Sc. Nat., 1824.
SMILIUM (pars generis). _Leach._ Zoolog. Journal, vol. 2, July, 1825.
CALANTICA (pars generis). _J. E. Gray._ Annals of Philosophy, vol.
x, (new series,) Aug. 1825.
THALIELLA (pars generis). _J. E. Gray._ Proc. Zoolog. Soc., 1848.
ANATIFA. _Quoy_ et _Gaimard_. Voyage de l"Astrolabe, 1826-34.
XIPHIDIUM (pars generis). _Dixon._ Geology of Suffolk, 1850.
(_Herm. et Foem._) _Valvis 12 ad 15: lateribus verticilli inferioris quatuor vel s.e.x, lineis incrementi plerumque convergentibus: sub-rostrum rarissime adest: pedunculo squamifero, rarissime nudo._
(Herm. and Fem.) Valves 12 to 15 in number: latera of the lower whorl, four or six, with their lines of growth generally directed towards each other: sub-rostrum very rarely present: peduncle squamiferous, most rarely naked.
Filamentary appendages, none: labrum, with the upper part highly bullate: trophi, various: olfactory orifices, more or less prominent: caudal appendages, uniarticulate and spinose, or none.
_Males_, parasitic at or near the orifice of the sack of the female or of the hermaphrodite: thorax enclosed within a capitulum, furnished with three or four rudimentary valves, or with six perfect valves: peduncle either short and distinct, or confounded with the capitulum: sometimes mouth and stomach absent, and cirri non-prehensile; sometimes mouth and cirri normal.
Generally attached to h.o.r.n.y corallines, in the warmer temperate seas over the whole world.
I have felt much doubt in limiting this genus: the six recent species which it contains, differ more from each other than do the species in the previous genera. Mr. Gray has proposed or adopted generic names for four of the species, and a fifth certainly has equal claims to this same rank. These genera have been founded almost exclusively on the number of the valves; and oddly enough, the numbers have generally been given wrongly, namely, in Scalpellum, Calantica, Thaliella, and Xiphidium.
Scalpellum blends through _S. villosum_ into Pollicipes; and this latter genus has an equal right with Scalpellum, to be divided into sub-genera, three in number. Hence, no less than eight genera might be made out of the twelve recent species of Scalpellum and Pollicipes, and their formation, in some degree, be justified; but, in my opinion, this inordinate multiplication of genera destroys the main advantages of cla.s.sification. At one time, I even thought that it would be best to follow Lamarck, and keep the twelve recent species in one genus; but considering the number of fossil species, I believe the more prudent course has been followed, in retaining the two genera Scalpellum and Pollicipes; more especially as I can hardly doubt, that several other species will be hereafter discovered.
Having so lately described in the Memoirs of the Palaeontographical Society, the fossil species, I will not here further allude to them, than to state, that out of the fifteen species therein described, _S.
magnum_ comes very close to the recent _S. vulgare_, and that several Eocene and Cretaceous species, such as _S. quadratum_, _S. fossula_, and _S. maximum_, are allied to _S. rutilum_ and _S. ornatum_. _Scalpellum villosum_, a recent species, has stronger claims than any other species to be generically separated; and its habits, in not being attached to h.o.r.n.y corallines, are also different, but the ident.i.ty of its Complemental Male with that of _S. Peronii_, and its numerous points of resemblance in structure with the other species, have determined me not to separate it. _Scalpellum Peronii_, _villosum_, and _rostratum_, in having a sub-carina,--in the rostrum being pretty well developed,--and in the Complemental Male being pedunculated, and furnished with a functional mouth and prehensile cirri, may be separated from _S.
vulgare_, _ornatum_ and _rutilum_; but even between these two little groups, _S. rostratum_ is in some respects intermediate, namely, in having three pairs of latera, and more especially in the rudimentary condition of the valves of its Complemental Male, and in the position in which the male is attached to the hermaphrodite. The three species in the second little group, namely, _S. vulgare_, _S. ornatum_, and _S.
rutilum_, are more nearly allied to each other in all their characters, especially in the characters drawn from their Males, than are the other three species. _S. ornatum_ and _S. rutilum_ are considerably nearer to each other than any other two of the species. Upon the whole I conclude that the six species must be thrown either into five or into four genera (the first three species making one genus), or all into one genus, and this latter has appeared to me the preferable course. The separation even of Scalpellum and Pollicipes, as already stated, is hardly natural.
The fact of these genera having existed from a remote epoch, and having given rise during successive periods to many species now extinct, is probably the cause that the few remaining species are so much more distinct from each other, than is common in the other genera of Lepadidae. Whenever the structure of the whole capitulum in the fossil species is well known, and as soon as more species, recent and fossil, shall have been discovered, then probably the genus Scalpellum will have to be divided into several smaller genera.
_Description._--The _Capitulum_ is much compressed, and generally produced upwards; it is formed of from twelve to fifteen valves, which are rather thin, and with the exception of _S. ornatum_, almost entirely covered by membrane, bearing spines: the valves are seldom locked very closely together. A sub-rostrum exists only in _S. villosum_, which species leads on to Pollicipes; in _S. vulgare_ the rostrum is rudimentary and hidden. The scuta, terga and carina, are much larger than the other valves: these five valves seem to differ essentially from the others in being at first developed under the form of the so-called primordial valves: the other valves commence by a small indistinct brown spot, very different from the hexagonal tissue of the primordial valves: I saw this very clearly in young specimens of _S.
vulgare_. At first, the scuta, terga and carina, grow exclusively downwards (and permanently so in most fossil species), and therefore the growth of the scuta and carina is in an absolutely opposite direction to what it is in Lepas, Paecilasma and Dichelaspis. After a short period the scuta are added to at their upper ends; the portion thus added, stands at a rather lower level, and projects in a rather different direction from the first-formed part of the valve, giving to it, in some respects, the appearance of having been broken and mended. This structure is common to _S. vulgare_, _S. rostratum_ and _S. Peronii_. The upper Latera (except in _S. villosum_) grow in the same manner, namely, at first exclusively downwards, and then both upwards and downwards. The rostral and carinal latera (with the same exception of _S. villosum_) have their umbones seated laterally, at opposite ends of the capitulum,--the umbones of the rostral latera being close to the rostrum, and those of the carinal pair close to the carina, and consequently their chief growth is directed towards each other. The carina in all the species, except _S. villosum_, is either bowed or angularly bent; in the latter case the lower half is parallel to the peduncle, and the upper half, extending far up between the terga, is parallel to their longer axes. In some of the species the carina is added to almost equally at both ends; in _S. ornatum_ it grows but little at the upper end, and to a varying degree in different individuals according to their age; in _S. rutilum_ the umbo is at the apex, and there is consequently no upward growth; lastly, in _S.
villosum_ the carina widening much from the apex to the basal margin, grows exclusively downwards, and a portion of the apex projects freely,--characters all common to the carina in the genus Pollicipes.
The upper latera occur in all the species; in the lower whorl there are either two or three pair of latera, in the former case the infra-median pair being absent. The latera differ considerably in shape in the different species.
The _Peduncle_ is generally rather short, and, with the exception of _S.
Peronii_, is covered with calcified scales. These scales are generally small, and placed symmetrically in close whorls, in an imbricated order, with each scale corresponding to the inters.p.a.ce between two scales in the whorls above and below. In _S. ornatum_, the scales are so wide, transversely, that there are only four in each whorl. In _S. villosum_, the scales are spindle-shaped and arranged somewhat irregularly in transverse rows, not very near to each other. New calcareous scales originate only round the top of the peduncle, and they continue to grow only in the few upper whorls; and as the peduncle itself continues to increase in diameter by the formation of new inner membranous layers and the disintegration of the old outer layers, the calcareous scales come in the lower part of the peduncle to stand further and further apart. In the earliest stage of growth there are no calcareous scales on the peduncle in _S. vulgare_; they first appear under the carina. Spines are articulated in great numbers on the surface of the peduncle in _S.
vulgare_, _S. Peronii_, and _S. villosum_, and very short ones on that of _S. rostratum_.
_Attachment._--All the species, except _S. villosum_, are attached to h.o.r.n.y corallines: the singular means of attachment in _S. vulgare_ will be described under that species, and is probably common to several of the other species. The larva in most, or in all cases, when it proceeds to attach itself, clings head downwards to the branch, and hence the capitulum comes to be placed upwards, with its orifice fronting the branch and the carina outwards. The sucking disc of the prehensile antennae of the larva, in the five species examined, was a little pointed, and in shape resembled the hinder hoof of a mule: this may perhaps be accounted for by the narrowness of the branches of the corallines, to which it has to adhere: a large circular disc, as in Lepas, would have been worse than useless: the ultimate segment in most or all the species, has on its inner side (the segment being supposed to be extended straight forward) a notch or step, bearing, I believe, two spines.
_Size and Colour._--Some of the species attain a medium size, others are small. The valves are generally clouded red or pink, but sometimes white.
_Mouth._--The various parts vary far more than in any genus. .h.i.therto described. The labrum is highly bullate, with the upper part forming a rounded overhanging projection, and with the lower part much produced, so that the mouth is placed far from the adductor scutorum muscle, and consequently the orifice is directed more towards the ventral surface of the thorax than in most other Cirripedes: on the crest of the labrum there are some very small teeth in several of the species, but not in all. The mandibles have either three or four main teeth, generally with either one or two small teeth intermediate between the first and second large teeth, and in the case of _S. Peronii_, with small teeth between all the larger ones. The maxillae have their edges furnished with many spines, and are either straight or have the inferior part prominent and step-formed. The outer maxillae have the spines on their inner edges either continuous or divided into two groups, of which latter structure we have not hitherto had any very well characterised example. The olfactory orifices are either highly or moderately protuberant.
In most of the species the prosoma is little developed, and the first cirrus is placed far from the second. The _Cirri_ are generally but little curled, and have elongated segments, with long, generally serrated spines: the first cirrus varies in proportional length; the second and third cirri have both their rami more thickly clothed with spines than are the three posterior cirri, the spines being generally arranged in three or four longitudinal rows: the cirri, however, of _S.
villosum_ in all respects resemble closely the cirri of _Pollicipes sertus_ and _P. spinosus_.
The _Caudal Appendages_ are uniarticulate, small, and clothed with spines: in _S. villosum_, however, differently from in all other allied forms, there are no appendages.
The _Stomach_, in those species which I opened, is dest.i.tute of caeca.
There are no filamentary appendages.
_Generative System._ The ova are nearly spherical, and remarkably large, as was stated to be the case in the introductory discussion, in which the larva of _S. vulgare_, in the first stage of development, was described: the ovigerous fraena are small. The testes are large, but the vesiculae seminales in some of the species extraordinarily small.
_Scalpellum ornatum_, and perhaps _S. rutilum_, are unis.e.xual; the other species are hermaphrodite, but most or at least some of the individuals, are furnished with Complemental Males. These latter are fully described under each species, so I will here only remark, that _S. ornatum_, which alone (excepting perhaps _S. rutilum_) is unis.e.xual, has less claim than the other species to be generically separated: we have seen also, in Ibla, that similar s.e.xual differences occur in two most closely allied species. It is very singular how much more some of the Males and Complemental Males in Scalpellum differ from each other, than do the female and hermaphrodite forms; this seems due to the different stages of embryonic development at which the males have been arrested. In the males, however, of _S. rostratum_, _S. Peronii_, and _S. villosum_, compared one with another, but not with the males of the other species, the parts of the mouth and apparently the cirri, resemble each other more closely, than do the same organs in the hermaphrodites. At the end of this genus I shall give a summary on the highly remarkable s.e.xual relations both in Scalpellum and Ibla.
_Distribution._--The species seem distributed over the whole world, but as far as we can trust our present scanty materials, are most common in the warmer temperate regions. The _S.
vulgare_ ranges from the Norwegian seas to Naples. Most of the species are inhabitants of deep water.
_Affinities._--In the preliminary remarks, we have seen how this genus blends into Pollicipes; and under the head of Oxynaspis, I have shown its close affinity to that genus. If, indeed, we take _Pollicipes spinosus_, and destroy all but six of the already minute and almost rudimentary latera, we shall, as far as the capitulum is concerned, convert it into a Scalpellum, closely similar to _S. villosum_. If we take any species of Scalpellum, (excepting _S. villosum_ and _S.
rutilum_,) and destroy all the valves, but the scuta, terga and carina, we shall convert it into an Oxynaspis. Lastly, I have shown under Ibla, that in several most remarkable peculiarities of structure, there is a manifest affinity between Scalpellum and that genus.
_Geological History._--Full details on this subject have been given in the Memoirs of the Palaeontographical Society. I will here only state, that the oldest known form of Scalpellum occurs in the Lower Green Sand.
[=T= SUB-CARINa NULLa.]
1. SCALPELLUM VULGARE. Pl. V, fig. 15.
SCALPELLUM VULGARE. _Leach._ Encyclop. Brit. Suppl., vol. iii, 1824.
LEPAS SCALPELLUM. _Linn._ Systema Naturae, 1767.
---- _Poli._ Test. utriusque Siciliae, Pl. vi., fig. 16. 1795.
POLLICIPES SCALPELLUM. _Lamarck._ An. sans Vertebres, 1818.
POLYLEPAS VULGARE. _De Blainville._ Dict. Sc. Nat., Plate, fig. 4.
1824.
SCALPELLUM LaeVE, var. _Leach._ Zoolog. Journal, vol. ii, p. 215, 1825.
---- SICILIae, var. _Chenu._ Ill.u.s.t. Conch. Pl. iv, fig. 9.
SCALPELLUM VULGARE, (et var.) _Brown._ Ill.u.s.t. of Conch., 1844, Pl. li., figs. 7 to 20.
_S. (Herm.) valvis 14, si rostrum paene rudimentale includatur: lateribus superioribus inaequaliter ovatis._
(Herm.) Capitulum with 14 valves, including the rudimentary rostrum: upper latera irregularly oval.