SEA-SLUGS, HETEROPODS AND PTEROPODS. 



209 



Fig. 41 8. Heli- WjMj) Fig. 420. ^fl Fig. 422. Bui- 

 cina. U. States. Acicula. la. U. States. 



Fig. 41 9. Britain. Fig. 421 . 

 Clyclostoma. Tornatella. 



United States. Britain. 



SEA-SLUGS. 



These have no shells, and many of them only slightly 

 resemble the Gasteropoda before described. See Fig- 

 ures 423-426. 



Fig. 427. At- 

 lanta. South 

 Atlantic. 



Fig. 423. Eolis. 

 Britain. 



Fig. 426. Tritonia, 

 Britain. 



HETEROPODS AND PTEROPODS. 



These live in the open sea. Some of them move in 

 immense swarms, miles in extent. Figures 428-430. 

 They much resemble the young of ordinary sea-snails. 

 They form the principal food of the Right Whale. One 

 kind, the Clio, Figure 430, is said to have upon the 

 head three hundred and sixty thousand suckers! 



