INVERTEBRATE ANIMALS. "25 



Stbattlj Cable Case, 



The Mark *i indicates specimens or other illustrations exliibitedin the Cases. 



Group 73.— Class PTEROPODA. yrrspov, a wing; Trobg, 

 a foot. Pelagic Mollusca, of small size, often found 

 swimming in countless myriads on the surface of the 

 deep, especially on calm evenings, from the tropics to 

 high latitudes. The shells are delicate and glassy. 

 The animals are very simply organised, and resemble 

 the minute but actively locomotive larvae of the Sea- 

 snails. Estimated number of species : recent, 73 ; 

 British seas, 5 ; fossil, several species of Conularia, and 

 other genera, from the Silurian upwards. 



^ Examples of about 40 species of Balaniinm, 

 CavoUna Hyahea, Clio, Lhnacina, and other 

 genera. 

 Series containing more than a few species of 

 Ptcropoda are rare in collections. For the 

 comparatively numerous examples here exhi- 

 bited, the collection is indebted chiefly to 

 Captains of merchant vessels sailing from 

 Liverpool, especially to Captains Whiteway, 

 Mortimer and Baker. 



Class GASTEROPODA." 



yaa-TYjp, the stomach ; ttov;, the foot. 



Head distinct, furnished with eyes and tentacles. Body 

 usually protected by a conical or spiral shell. Lower 

 part of the body formed into a thickened, expanded, 

 creeping disc or foot. This class includes all the land 

 and most of the fresh-water and marine univalve 



