GASTEROPODA. 157 



Animal with a "broad creeping disk like the limpet ; proboscis armed with 

 cartilaginous jaws, and a long linear tongue ; lingual teeth 3 ; median small, 

 laterals large, with dentated hooks ; uncini 5, trapezoidal, one of them erect 

 and hooked. No eyes, or tentacles. Branchiae forming a series of lamellae 

 between the foot and the mantle, round the posterior part of the body. The 

 heart is central, and elongated like the dorsal vessel of the armelidcs ; the 

 sexes are united ; the re-productive organs are symmetrically repeated on each 

 side, and have two orifices ; the intestine is straight, and the anal orifice pos- 

 terior and median. 



Distr. More than 200 species are known ; they occur in all climates 

 throughout the world ; most abundant on rocks at low-water, but frequently 

 obtained by dredging in 10 25 fathoms water. Some of the small British 

 species range as deep as 100 fms. (Forbes.) W. Indies, Europe, S. Africa, 

 Australia, and New Zealand, California to Chiloe. 

 Fossil, 24 sp. Silurian . Brit., Belgium, &c. 



Sub-genera* Chiton, (Syn., lophurus, Poli. Radsia, callo-chiton, 

 ischno-chiton, and lepto-chiton, Gray). 



Ex., C. squamosus. PI. XT., fig. 28. Border tessellated. 

 Distr. Brazil, W. Indies, Newfoundland, Greenland, Brit., Medit., Cape, 

 Philippines, Australia, New Zealand, W. America. 



Tonicia, Gray. C. elegans. Margin bare. Distr. Greenland, C. Horn, 

 New Zealand, Valparaiso. 



Acanthopleura, Guilding. C. spinosus. PI. XT., fig. 29. Margin covered 

 with spines, or elongated scales. Syn. Schizo-chiton, corephium, plaxiphora, 

 onycho-chiton, enoplo-chiton, Gray. Distr. W. Indies, C. Horn, Falklands, 

 Africa, Philippines, Australia, New Zealand, Valparaiso. 



Mopalia, Gray. C. Hindsii. Border hairy. ' Distr., W. America, Talk- 

 land Islands. 



Katharina, Gray, C. tunicatus. Mantle covering all but the centre of the 

 plates. Distr. New Zealand, W. America. 



Cryptochiton, Gray, " Saw-dust chiton.". C. amiculatus. Valves covered 

 with scaly epidermis. Syn., cryptoconchus, Sw. Amicula, Gray. Distr., Ca- 

 lifornia, New Zealand. 



Acanthochites, Leach. C. fascicularis. PI. XI., fig. 30. Border orna- 

 mented with tufts of slender spines, opposite the plates. Distr., Brit., Medit. 

 New Zealand. 



Chitonellus, Lam. C. fasciatus, Quoy. PL XI., fig. 31. Border 

 velvety ; exposed portion of the plates small, distant ; apophyses close to- 



* The sub-genera of Mr. Gray are founded on the form of the plates of inser- 

 tion ; they are described in detail in the proceedings of the Zoological Society. Dr. 

 Middendorf employs the number of the branchial lamince for distinguishing the 

 sections. 



