104 PTEROPODS. GASTEROPODS. 



The PTEROPODS have likewise no ordinal section ; the 

 members of the class, which is a small one, being distributed, 

 in the manner of the Cephalopods, into certain genera; and 

 the few established by other authors, on a more minute 

 analysis of their forms, are reduced under these as of se- 

 condary importance. All the Pteropods are marine, float- 

 ing at or near the surface, and having no power to creep 

 along a solid base from their want of a foot. In conse- 

 quence of their fragility and minor bulk they avoid the 

 shore, and hold the high seas as a field for their possession. 

 We have no British example of the class. The Clios and 

 Limacines (Fig. 13) swarm in the Arctic Seas, where, though 

 less than a common snail, they fur- 

 Fi S- 13 - nish an abundant food to the whale ; 



the Cymbulies, so named from its 

 canoe or slipper -like shape ; the 

 Pneumodermon, a name which signi- 

 fies that the branchiae are attached 

 to the skin or surface ; the Hyales, 

 natives of the Mediterranean ; the 

 Cleodores, which belong to tropical 



seas,' these are the genera which Cuvier ranks under the 

 class ; and to them he is of opinion may be added a 

 small fossil shell of a globular shape, and very thin texture, 

 divided by a narrow transverse fissure somewhat widened 

 in front. This was discovered by Defrance, and is named 

 Pyrgo. Of all these it may be remarked that few, some- 

 times only one or two, species belong to each genus ; and 

 that the shell, which is sometimes wanting or entirely 

 membranous, has a peculiarly transparent, brittle, and vi- 

 treous texture, with a certain degree of anomaloushess in 

 its form, which intimates that it belongs to an animal of 

 abnormal character and habits. 



The GASTEROPODS (Fig. 14) are a numerous class of 

 mollusks, of whose character the slug 

 u - and snail, familiar to every one, give 



a good idea. They are generally, 

 like the latter, covered with a shell, 

 but many are naked ; and they in- 

 habit, some the deep sea, the shore, 

 the river, the lake, the marsh, and 

 the shady groves as well as the 

 parched sands. To fit them for 

 such dissimilar localities, the Creator 

 has varied the position and the structure of the respiratory 



