136 POPULAR CONCHOLOGY. 



Order I. 



PTEROPODA.* 



The animals of this order have no feet to 

 crawl with, but are free and floating, and have 

 two opposite and similarly constructed fins 

 adapted for swimming. Some genera only 

 are furnished with a thin, cartilaginous, or 

 horny shell. The greater part are animals of a 

 small size. There are six genera, as follows : 



1. Hyal^a. — Shell horny, transparent, 

 ovate, globular; tridentated posteriorly, open 

 at the summit and at the 

 two posterior sides. Ani- *5§|^^ 

 mal, body covered by a 

 shell ; head very indistinct ; no eyes. — 17 spe- 

 cies recent, 1 fossil. 



These shells are brought from the Mediter- 

 ranean and Atlantic. Their trivial name in 

 England is Venus' Chariot. 



2. Clio. — No shell. Animal, body oblong; 

 head provided with several tentacula ; two eyes 



* Les Pteropodes, Lamarck. 



