632 



M O L L U S C A. 



The mouth is situated between the arms at the 



Molluscs, form. 

 " ' f**^ base. 



All the miimals of this -class are inhabitants of the 

 sea, and they are permanently attached to rocks and 

 stones. Three genera are known, which are probably 

 the types of as many orders. 



Lingula. 1 Lingula. The valves of the shell of the species 



which constitutes this genus, were .first figured by Seba, 

 together with the peduncle by which they are support- 

 ed. Linna;us having seen only one valve, conjectured 

 that it belonged to the Patella, and named it P. unguk. 

 Chemnitz examined both valves, without the>peduncle, 

 and pronounced 'them ^connected -with the genus Pinna. 

 Bugiere, aware of Seba's figure, contemplated the 

 formation of the new genus for its reception, which La- 

 marck executed. M. Cuvier afterwards dissected one 

 of the individuals, which Seba had possessed, and un- 

 folded characters in its organization snfficjent notconly 

 to warrant the construction of a new genus .but a new 

 class. 



The peduncle of the Lmgula in cartilaginous, hav- 

 ing the inferior ends of the two oval valves attached to 

 its extremity, the other end 'being fixed to foreign bo. 

 dies. The valves are destitute of teeth, or an elastic 

 ligament, and are opened chiefly by the arms when 

 pushed out, and closed by the adductor muscles, which 

 are capable of acting in an oblique direction, and of 

 giving to the valves a considerable degree of lateral mo- 

 tion. The margin of the cloak, which is double like 

 the shell, is fringed with fine hairs. The .arms are 

 fleshy in their substance, conical, elongated and com- 

 pressed in their form, and ornamented on the external 

 surface with thickset fringes or tentacula. The mouth 

 is situated between the arms at their base,, and is simple. 

 There is no enlargement of the alimentary canal, which 

 can be regarded as a stomach, and the anus is a simple 

 aperture situated on the side. There are marked in- 

 dications of salivary glands and a liver. The blood is 

 conveyed to the gills by two vessels, which are divided 

 at the separation of the lobes into two branches, one 

 of these going to the half of one lobe, and another to 

 the opposite half of the other lobe. Two systemic 

 veins occupy a similar position, and .return the aerated 

 blood to the two lateral systemic ventricles. The gills 

 themselves are arranged in a pectinated form on the 

 inner surface of each lobe of the cloak. There is no- 

 thing known of the nervous or reproductive systems of 

 this animal. 



The Lingula unguis is the only species of the genus, 

 and appears to be confined to the Indian seas. Some 

 petrifactions have recently been referred to this genus; 

 but in the absence of all vestige of the peduncle, we do 

 not consider .the mere form of the shell as furnishing 

 characters sufficiently obvious and precise to warrant 

 such arrangement. 



Tere-bra- "' Terebratiila. The muscular peduncle of this ge- 

 tula. nus passes through a perforation in the largest valve. 



The, arms are shorter than those of lingula, and forked 

 at the extremities. They are supported within by nu- 

 merous arcuated plates. 



There is one recent species described in the article 

 CONCBOLODY, v.ol. vii. p. 36, genus xxxix. and figured 

 tab. ccvi. fig. 2, as T. vitrea. It appears, however, to 

 be the T. cranium of Muller, figured in Zoologia Da- 

 nicn, tab. Jtciv. f. 1. Although we can boast of only 

 .one recent species of this genus, our rocks abound in 

 many others which are extinct. Mr. Sowerby, in his 

 valuable work, Mineral Couchology, now publishing, has 

 given excellent representations of several of these. He 

 Has been able, from an attentive examination of their 



form, to construct several new genera, and, from a dig. 

 section of the cavity, to unfold the remains of the spiral 

 arms. 



3. Crinptts. In this genus, first instituted by Poll, 

 one of the valves is membranaceous and flat, and ad- 

 heres to stones, and the other is flatly conical, and re- 

 sembles a Patella. The arms nearly resemble those of 

 Lingula. The ovarium, according to Muller, is double 

 and branched, and the eggs are round. 



The Criopus anomalus is described and figured by 

 Muller under the name Patella anomala, in the Zuolo- 

 gia Danica, tab. v. f. 1 8, and by us, for the first 

 time, as a native of Britain, in the article CONCHOLOGY, 

 vol. vii. p. 65, genus i. sp. 7, P. distorta, tab. cciv. 

 fig. 4. 



It is to be regretted that so little progress has been 

 made in the examination of the animals of this class. 

 We are still ignorant of their nervous system, and their 

 mode of propagation ; and when these and their other 

 organs shall be more carefully investigated, many new 

 divisions will probably be necessary, as the species in 

 Crease in number. 



CLASS VII. CIRRHIPODA. 



The genus Lepas of the Linnean system, after hav- CIRHHI. 

 ing been subdivided .into different genera, has at length, PODA. 

 by the:efforts of M. Lamarck, been formed into a dis- 

 tinct class. The animals which it includes are pro. 

 tected by a cloak, strengthened by testaceous plates, to 

 which the body adheres by one or more muscles. The 

 head consists of a slight eminence attached to the an- 

 terior -portion of the body, and, when in the natural po- 

 sition, near the inferior .margin. The body is followed 

 by a tail, supporting six feet on both sides, each of 

 which consists of a short stem, which divides into two 

 tapering jointed fringed filaments ; these, by their mo. 

 tion towards the mouth, bring the water and its con- 

 tents within the sphere of that organ. The tail termi- 

 nates in a conical tubular body, which has improperly 

 been termed a proboscis. 



The nervous system consists of a cord encircling the 

 gullet, and giving out filaments to the mouth; its two 

 ends running along the belly and tail, and uniting at 

 the base of each pair of feet to form a ganglion, and 

 give off filaments. 



The mouth is furnished with an obvious upper lip, a 

 pair of maxillae on each side, with the rudiments of pal- 

 pi. Ellis says, " the mouth appears like that of a con- 

 tracted purse, and is placed in front between the fore 

 claws. In the folds of this membranous substance 

 are six or eight horny lamina;, or teeth, standing erect, 

 each having a tendon proper to direct its own motion. 

 Some of these teeth are serrated, others have tufts of 

 sharp hairs instead of indentations on the convex side, 

 that point down into the mouth ; so that no animalcule 

 that becomes their prey can escape back." The -gullet 

 is very short, and enters into a stomach, having two 

 caeca and glandular walls, which serve as a liver. The 

 intestine is short and simple, and terminates behind at 

 the base of the caudal appendage. There are two sali- 

 vary glands attached to the stomach. The gills are 

 conical bodies, situated at the base of the feet. The 

 organs of circulation are imperfectly understood. Poli 

 observed the motion of the heart, but the vessels which 

 are connected with it are unknown. 



The organs of reproduction appear, according to 

 Cuvier, to consist of an ovarium giving out an oviduct, 

 which traverses a body considered as a testicle, and 



