58 SHELLS AND SHELL-FISH. PART 1. 



for although this genus has been excluded by some 

 writers, and separated from Fissurella, &c., in a dis- 

 tinct tribe, yet this is evidently doing a violation to 

 nature. None of the genera in our present group pos- 

 sess spiral shells ; for although Haliotis is obviously 

 intermediate between the Phytophaga and the Scuti- 

 branchia, its preponderating character, both as regards 

 the animal and the shell, appears to us in favour of its 

 being placed as the last of the turbinated families, rather 

 than as the first of the present group. Thus restricted, 

 the Scutibranchia will contain Patella, Siphonaria, 

 Fissurella, Emarginula, Parmophorus, Capulis, &c., 

 together with the singular genus Hipponyx, of which 

 we shall have occasion to speak hereafter. Magilis 

 and Siliquaria evidently disturb this series, yet open a 

 direct path to the Dithyra, or bivalves. 



(50.) The CYCLOBRANCHIA, according to Cuvier, "have 

 the branchia resembling small lamellae, or little pyra- 

 mids, forming a cordon more or less complete under the 

 borders of the mantle, very nearly the same as the In- 

 fer obranchia," from which, however, he separates them 

 on account of their different system of reproduction : 

 c ' the heart," he continues, <e does not embrace the 

 rectum, but its situation varies ; the stomach is mem- 

 branaceous, and the intestines very long." The only 

 genera placed by Cuvier in this group, are Patella and 

 Chiton. The first, however, is so evidently connected 

 to the Scutibranchia in all other points of organisation, 

 setting aside the shell, that we have no hesitation in 

 adopting the theory of Lamarck, who unites the genera 

 Phyllidia and Diphyllidia to Chiton, particularly as this 

 arrangement at once opens a direct passage to the Tec- 

 tibranchia. The shells of the chitons, which thus 

 become the types of the Cyclobranchia, are boat-shaped 

 and multivalve, the valves being disposed transversely 

 upon the back of the animal, and folding over each 

 other like a coat of mail. 



(51.) The TECTIBRANCHIA, to which we are conducted 

 by Lamarck, form a most natural group. It is peculiarly 



