112 PTEROPODA. 



Class PTERO'PODA*, (PTERO- 

 PODES) Cuvier. 



BODY gelatinous, spiral, oval, or conical : head less distinct 

 in those kinds which have shells than in the naked kinds : 

 mouth placed at the bottom of a cavity between the foot-lobes, 

 and armed with a spinous tongue or odontophore : tentacles in 

 the naked kinds only, in some species of which they are fur- 

 nished with cup-shaped suckers: eyes in Clio, Clione, and 

 Cymbuiia (De Blainville), in Clione (Leach), wanting in all 

 the Pteropods (Rang and Souleyet): foot expanded into two 

 wing-like lobes, one on each side, which are used chiefly for 

 swimming or floating: gills internal in the testaceous, and 

 external in the shelless kinds. Hermaphrodite. 



SHELL (in those kinds that possess one) univalve, thin, 

 vitreous or membranous, forming a reversed coil, a nearly glo- 

 bular and often tricusped case, a sheath, or a slipper. 



These : .are small gregarious mollusca, inhabiting the 

 wide ocean, where they swim or rather float in a reversed 

 position, by flapping the wing-like lobes of the foot. 

 They are strictly pelagic, and never of their own accord 

 come near the land. Indeed their power of locomotion 

 is very limited, and consists of a jerking action, by 

 which they move up and down in the water, either in a 

 straight line or obliquely ; this appears to be effected 

 by opening and closing their foot-lobes. It has been 

 stated that their habits are nocturnal or crepuscular; 

 and for this reason they have been called Neptune's 

 moths instead of butterflies, and accused of leading a 

 gay and dissipated life, like midnight roisterers. D'Or- 



* Foot wing-like. 



