PTEROPODA. 



119 



Gcm^s 20.— CHITONELLUS Lamarck. 



Generic Character Body creeping, elongated; middle 



of the back provided in its entire length with a multivalve 

 shell, of which the alternate pieces, for the most part longi- 

 tudinal, are connected by their extremities, in the form of a 

 band ; sides naked ; branchiae disposed around the body ; 

 foot cleft longitudinally by a deep furrow. 



The testaceous plates of this genus are never joined like those of 

 the Chiton, so that the animal can move in every direction. Upon the 

 contraction of the animal after death, however, these valves become 

 nearly united. 



Chitonellus striatus. — The Striated Chitonellus. 

 Plate XIV. fig. 10. Each valve with striae radiating from 

 its apex; the margins serrated; the base of the last valte 

 obtuse. Inhabits the seas of New Holland. 



TRIBE VII. — TRITOXACEA. 



With external branchiae, placed over the mantle on the 

 back or sides. Destitute of shells, and respiring water. 

 An extensive and highly interesting tribe of slug-like marine 

 animals, of which the genera, not being furnished with shells, 

 do not properly enter into a merely conchological arrange- 

 ment. 



OEDER V.-PTEPiOPODA. 



Animals destitute of a foot for locomotion, and of arms 

 for seizing their prey; but provided with two opposite and 

 similar fins fitting them for swimming; body free and float- 

 ing; some of them are destitute of shell. 



Genus \.—QYMB\]\AK.—Cuvler. 



Generic Character Body oblong, gelatinous, pellucid, 



enclosed in a shell; head sessile; two eyes, and two re- 



