GASTEROPODA. 103 



Genus 24 — PATELLA Linnmus. 



Generic Character. — Body completely covered by the shell ; 

 bead with two acute tentacula, and the eyes situated at their ex- 

 terior base ; branchiae placed under the ntiantle and around the 

 body ; anal and generation orifices situated on the right anterior 

 side. — Shell univalve^ not spiral, concave within, simple, entire, 

 with the vertex anteriorly inclined, and imperforate. 



The anterior side of the shell, is that to which the summit is inclined, the 

 impression of the animal's head can easily be distinguished internally on 

 that side. 



Patella vulgaia.— The Common Patella, or Limpet. Plate 

 XIV. fig. 15. Oval, conic, or a little depressed ; outside green 

 or brown, sometimes radiated with various colours ; having di- 

 vergent striae and concentric wrinkles ; inside glossy, iridescent, 

 with yellow or fawn-coloured, purple, blue, or brown radiations. 

 Two inches long. Inhabits the coasts of Europe. 



Genus 25. — CHIT 01^. -LinncEJis, 



Generic Character. — Body creeping, ovate-oblong, convex^, 

 round at both extremities ; marginated with a coriaceous skin ; 

 the back covered by a longitudinal series of testaceous, trans- 

 verse, imbricated, and moveable plates ; head before, sessile, 

 with the mouth placed below ; destitute of tentacula or eyes ; 

 branchife placed round the body, under the margin of the skin ; 

 and orifice at the posterior extremity. 



The species of this genus are in much obscurity, and of difficult solution, 

 the absence or presence of granulations, strise, and punctures, are certainly 

 of much use, but the only certain test, is an examination of the sides of the 

 valves, which, however, cannot be accomplished without taking the speci- 

 men to pieces. The sides of the valves are always provided with a certain 

 number of serrated teeth, these seem to be permanent characters in each 

 rspecies. See Plate 1. fig. IL 



Chiton fascicularis. — The Fasciculated Chiton. Plate 

 XIV. fig. 13. Eight imbricated valves, nearly smooth, slightly 

 carinated, and rounded at the margins, with a thick tuft of hair 

 between the junction of the valves^ having five on the top of the 

 upper valve, and three on the base of the lower one. Three- 

 fourths of an inch long. Inhabits the British coasts. 



