The peduncle consists of the two external membranes of the integuments of the body. The cuticle covers its surface, and even the base by which it adheres. The true skin is covered on its central aspect with numerous muscular threads. The summit of the peduncle next the body is covered with the inner membrane of the cloak, through which, however, there is a perforation, cor responding to a large vessel which descends along one of the sides of its central cavity. This cavity, in the Lena& anatifera, Cuvier found filled with a white cellular substance soaked with muscus. Ellis, on the other hand, found the peduncle of what has usually been re garded as the L. aurita " full of a soft spongy yellow substance, which appeared, when magnified, to consist of regular oval figures, connected together by many 4 S 2 small fibres, and no doubt arc the spawn of this ani mal." This view of the subject entertained by Ellis may, upon investigation, lead to the conclusion, that the cavity of the peduncle and its lateral vessel are connect Avith the reproductive organs. It would be desirable to have the branched peduncles dissected with care, as a knowledge of their structure might throw some light on the mode of growth of these animals.
I. Family. This group is characterized by the body being protected by five tcstaceous plates, and by the pe duncle being naked. It includes the hollowing genera.
1. Lepas. The two lateral plates at the summit of the shell are very large, nearly covering the whole of the compressed body, and having attached to it the large ad ductor muscle. The two valves which protect the sides of the tail arc much smaller, and somewhat trian gular, while the dorsal one is narrow and convex ex ternally. The branchix arc four in number, two on each side of the body, near the origin of the fit st pair of feet. The British species are four in number, L. anatifera, an scrifcra, sulcata, and jerscicularis.
2. Otion. Tnis genus was instituted by our zealous and intelligent friend Dr. Leach, whose labours have greatly contributed to improve the classification of the genera of this class. The body is but slightly com pressed, and the valves are very small and distant from one another, the body being chiefly covered by its membranaceous cloak. The interior part of the cloak terminates in two tubular appendages, through which the water escapes which has been taken in at the oral aperture, and has passed along the surface of the gills. The gills arc sixteen in number, eight on each side. The first pair on each side resembles those of the Lepas, the remaining six are attached to the base of the feet. There are two British species. 1. O. auritu, Cuvier, Mem.
des Anatifes. Fig. 12, 13. A specimen of this was found on the Dawlish coast, Devon, by Mr. Comyns. 2. O. cornuta, taken alive from the bottom of a trans sport stranded on the coast of Devon, by Montagu, and described and figured by him, Linn. Trans. vol. xi. p. 179, tab. xii. f. I.
3. Cineras. This genus was likewise instituted by Dr. Leach. The valves are equally minute and remote as in the preceding genus, but there is here no appear ance of tubular appendages to the cloak. The C. mem branacca, first described and figured by Montagu, Linn. Trans. vol. xi. p. )82, tab. xii. f. 2. is the only species known to inhabit the British seas.
2. Family. In this family the tcstaceous valves are numerous, greatly exceeding five. It consists of two genera.
1. Scalpellum. The testaccous valves are thirteen in number, and invest the body. The peduncle is covered with corneous wrinkles, having hairy interstices. The S. vulgare, the Lepas scalpellum of British authors, is the type of the genus.
2. Pollieipea. The tcstaceous valves are ten in num ber, with numerous scales investing the base of the pe duncle near the body. The P. vulgaris, or Lepas pol liceps, is the type of the genus.
In this order the body adheres directly to foreign substances, without the intervention of a tubular stalk. The adhesion is effected in some by the coriaceous cloak, in others by a layer of testaceous matter. The testaceous covering usually assumes a conical form, the base being attached to rocks or other substances, and the apex truncated and open, as an entrance for the water. This cone consists of six valves, closely con nected together, but capable of being disjoined by maceration, especially when young. In old shells, where the valves have attained their full growth, they appear to become cemented together, so that it is very difficult to effect their separation. The valves are so arranged, that one protects the belly, another the back, and two on each side the lateral parts. In some genera, all these valves are so united, that the lines of separa tion are not perceptible, while in others the double lateral valves only arc incorporated. Each valve con sists of an elevated and depressed portion. The elevat ed portion is conical, with its base at the adhering part of the shell, while the depressed part of the same form has the base at the mouth. The former consists of co nical vertical tubuli, while the latter appears solid. 'When the base is tes,aceous, it is either solid, or consists of horizontal tubule, radiating from a centre united by a simple layer, exhibiting concentric circles.