104 PTEROPODA. 



Genws 26. — CHITONELLUS Lamarck. 



Generic Character. — Body creeping, elongated; middle of the 

 back provided its entire length with a detached multivalve shell ; 

 the alternate pieces for the most part longitudinal ; sides naked ; 

 branchiae disposed around the body ; foot cleft longitudinally by 

 a deep furrow. 



The testaceous plates of this genus are neverjoinedlike 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. lig. 10. Each valve with striae radiating from its apex; 

 the margins serrated ; the base of the last valve obtuse. Inhabits 

 the seas of New Holland. 



TRIBE VII. TRITONACEA. 



With exterior branchise, placed over the mantle on the back or 

 sides. Destitute of shells. 



ORDER v.— PTEROPODA. 



Animals destitute of any foot for locomotion, and of arms for 

 seizing their prey ; provided with two opposite and similar fins 

 fitting them for swimming ; body free and floating. 



GenMsl.— CYMBULIA Cuvier. 



Generic Character. — Body oblong, gelatinous, pellucid^ in- 

 closing a shell ; head sessile ; two eyes, and two retractile ten- 

 tacula ; mouth with a retractile proboscis ; two opposite, oblong- 

 ovate, branched wings, connate at their posterior base. — Shell 

 gelatino-cartilaginous, transparent, and oblong ; apex truncated ; 

 the aperture lateral. 



Cymbulia Peronii. — Peron's Cymbulia. Plate XIV. fig. 

 6. Somewhat gelatinous, or cartilaginous ; very transparent crys- 



