M L L U S C A. 



633 



both the canals unite in a common tube, which tra- 

 verses the caudal appendage, and opens by a small 

 pore at its extremity. This aperture Cuvier regards as 

 simple, but Ellis observes of the whole, " it is of a tu- 

 bular figure, transparent, composed of rings lessening 

 gradually to the extremity, where it is surrounded with 

 a circle of small bristles, which likewise are moveable 

 at the will of the animal. These, with other small 

 bain on the trunk, disappear when it dies." There is 

 probably no union of individuals, each being perfect 

 hermaphrodites. 



The rapidity of growth which these animals exhibit 

 is truly astonishing. A ship's bottom becomes covered 

 with them in a few months, and the spawn of some 

 kinds deposited on a feather, as stated in the memoirs 

 of the Wernerian Society, voL ii. p. 2*3, will become 

 unfolded, and attain maturity before the feather exhi- 

 bits any symptoms of decay. 



The animals of this class are all inhabitants of the sea, 

 and are all fixed to other bodies. Many of them, how- 

 ever, are attached to floating wood, and others to the 

 kin of marine animals, so that they enjoy all the ad- 

 vantage* of locomotion without the exercise of the ex- 

 ertion requisite for its production. Their remains are 

 seldom found in a fossil state. Some of the species 

 have been used as food. In taking a view of the ge- 

 nera we hall distribute them, as formerly, aftiT tin- 

 manner of Ellis, Phil. Trtuu. vol. 1. p. b IS, into pedun- 

 culated and sessile. 



ORDER I. PBDU\CULATED. 



The oscnlial character of this order consists in the 

 body being supported by a peduncle, the lower part of 

 which i- permanently fixed to oilier bodies. 



The cloak consist* of three membranes. The ex- 

 ternal one is the cuticle, and invests the whole external 

 surface of the animal. Underneath this is the true skin, 

 in which are formed the testaceous plates that protect 

 the body. Thete plates or valves are evidently formed 

 in the came manner as common shell, the layers of 

 growth being indicated by the stria? on the surface. 

 The inner membrane forms a sac for the body it.-tlf. 

 This bag is closed on all aides except opposite to the 

 tail, where there is a slit through which the feet are 

 protruded. 



The peduncle consists of the two external membranes 

 of the integuments of the body. The cnticle 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 corres- 

 ponding to a large vessel which dctccnds along one of 

 the sides of its central cavity. This cavity, in the 

 Lepai amalifera, Cuvier found filled with a white cellular 

 substance soaked with muscus. Ellis, on the other 

 band, 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 

 small fibre*, and no doubt are 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 con- 

 nected with 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 ani- 



VOL. xir. PART ii. 



1. Family. This group is characterised by the body Mollusca. 

 being protected by five testaceous plates, and by thepe- 

 duncle being naked. It includes the following genera. 



1 . Lepas. The two lateral plates at the summit of the 

 shell are very large, nearly covering the whole of the 

 compressed bod} 1 , and having attached to it the large ad- 

 ductor muscle. The two valves which protect the 

 sides of the tail are much smaller, and somewhat trian- 

 gular, while the dorsal one is narrow and convex ex- 

 ternally. The branchiae are four in number, two on 

 each side of the body near the origin of the first pair of 

 feet. The British species are four in number, L. ana- 

 tij'era, anscrifera, sulcala, and fascicularis. 



2. Otion. This genus was instituted by our zealous Otion. 

 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 inferior 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 are 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 . 0. aurita, Cuvier, Mem. 

 det Analijet. Fig. 12, 13. A specimen of this was 

 found on the Dawli>h coast, Devon, by Mr. Comyns. 

 2. O. carnnla, 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. 1. 



3. Cinerat. This genus was likewise instituted by Qneru. 

 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. meni- 

 liranacca, first described and figured by Montagu, Linn. 

 Tram. vol. xi. p. 1 82, tab. xii. f. 2. is the only species 

 known to inhabit the British seas. 



2. Family. In this family the testaceous valves are 

 numerous, greatly exceeding five. It consists of two 

 genera. 



1. Scalpcllum. The testaceous valves are thirteen in Scalpcllum. 

 number, and invest the body. The peduncle is covered 



with corneous wrinkles, having hairy interstices. The 

 S. vulgare, the Lepa* tcaljiiiiuni of British authors is 

 the type of the genus. 



2. Poilicipet. The testaceous valves are ten in num- Pollieipeg. 

 ber, with numerous scales investing the base of the pe- 

 duncle near the body. The P. vulgar it, or Lepa* pot' 



licept, is the type of the genus. 



II. ORDER. SESSILE. , 



In this order the body adheres directly to foreign Senile. 

 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 awumes a conical form, the 

 base being nttaclu d to rocks or other substances, and 

 the apex truncated and open as an entrance far the 

 water. Thin 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 tin-back, 

 and two on each side the lateral parts. In some go. 

 4 L 



