CLASS. 



PTEROPODA. 



We have thought it desirable, in order to give a general 

 view of the family, and at the same time to save as much 

 space as possible, to assemble such genera of the Ptero- 

 poda as we are able to illustrate, in two plates. This is a 

 small family and may be more easily illustratedconsecutively, 

 particularly as the various genera of which it is composed 

 resemble each other to a great degree. Scarcely any of 

 the Pteropoda were known to Linnean writers on conch- 

 ology, the only one that we recollect in any Linnean work 

 before the modern improvements of Cuvier, Lamarck, &c. 

 being the Hyalcea tridentata which is in such works named 

 Anomia tricuspidata : than which nothing could be much 

 more absurd, since, independently of the important dif- 

 ferences existing between the animals, it is well known 

 that the Linnean Anomiae are bivalves, while the Hyalaea 

 and all the Pteropoda are univalves. Cuvier in his Me- 

 moires sur les MoUusques, has shown that the Pteropoda 

 are a separate family or class, distinguished by certain 

 peculiarities, the organs of locomotion being shaped like 

 wings, the whole of them being free swimmers, and their 

 shells in general having a peculiarly transparent, brittle, 

 and vitreous character. The genera of this family which 

 we shall here illustrate, are Hyalaea, Cleodora, Limacina, 

 Creseis, Vaginula, Cuvieria, and Cymbulia. They are 

 mostly found swimming about in the sea in all climates, 

 and in some they abound to such a degree that thev are 

 said to be the chief food of the cetaceous mammifera. 

 Besides the above-named genera, there are others belong- 

 ing to the same family, which are, however, destitute of 

 shell; we suspect, moreover, that the little transparent 

 shell called Dentalium Gadus, by Montagu, will prove, 

 when its animal is known, to belong to this family. The 

 whole of the Pteropoda are marine, and they appear to 

 belong to all climates. 



