1901.] NATURAL SCIEXCES OF PHILADELPHIA. 511 



Peck, and it also differs iu being relatively larger and mucli nearer 

 the anterior margin of the casque. Beyond the pallial gland the 

 mantle cavity narrows and again enlarges to form the space 

 surrounding the visceral mass, kidney and heart. Peck's figure of 

 C. calceola represents the foot as extending to the anterior border 

 of the casque, while in G. vitrea this organ is relatively much 

 larger and projects beyond the shell almost half its width. Three 

 sets of muscles operate it as in the other species of the genus, and 

 a large number of pigment spots, probably sensory in function, are 

 scattered along its maro-iu. 



