*258 MOLLUSCA. 



wise widely opened above the head. A branchial comb is symmetrically 

 tenarranged on each side ; the eyes are on the external base of the conical 

 tentacula, and the sides of the foot are furnished with a range of filaments. 

 There are two other genera, Emaryinula and Parmophorus. 



ORDER IX. 



CYCLOBRANCHIATA. 



THE branchiae of the Cyclobranchiata resemble small lamellae, or h'ttle 

 pyramids, forming a cordon more or less complete 

 under the borders of the mantle, very nearly as in the 

 Inferobranchiata. Their heart varies as to situation ( 

 But two genera of this order are known, in both of 

 which the shell never approaches in the least to the 

 turbinated form. 



PATELLA, Linnaeus. 



The entire body covered with a shell, formed of a single piece, in the form of 

 a broad-based cone ; a cordon of little branchial lamellae under the margin of 

 the mantle; the head is furnished with a thick and short snout, and two 

 pointed tentacula, on the external base of which are the eyes ; the mouth is 

 fleshy, and contains a spiny tongue, which inclines backwards, and is reflected 

 deeply in the interior of the body. 



CHITON, Linnaeus. 



A range of testaceous and symmetrical scales along the back of the mantle, 

 but not occupying its whole breath ; edges of the mantle coriaceous, and 

 furnished either with a naked skin or h'ttle scales, which give it the appear- 

 ance of shagreen, or with spines, hairs, or setaceous fasciculi. Under these 

 edges, on each side, is a range of lamellar, pyramidal branchiae ; and before, 

 a membranous veil on the mouth supplies the want of tentacula. 



A few small species are found on the coast of France ; very large ones 

 abound in the seas of hot climates. 



CLASS IV. 



ACEPHALA. 



THE Acephala have no apparent head ; but a mere mouth concealed 

 in the bottom, or between the folds of their mantle. The latter is 

 almost always doubled in two, and encloses the body as a book is 



