LAMELLIBRANCHIA. 



223 



They much resemble the young of ordinary Sea Snails. 

 They form the principle food of the Right Whale. 

 One kind, the Clio, Figure 428, is said to have upon 

 the head three hundred and sixty thousand suckers ! 



Fig. 426. — Hylea. 

 Atlantic. 



Fig. 427. — Limacina. Fig. 428. — Clio. 

 South Polar Seas. Arctic. 



LAMELLIBRANCHIA. 



These have no distinct head, breathe by plate-like 

 jills, usually two pairs, and have a bivalve shell. 



Fig. 429. — One valve of a Bivalve Shell, showing the names of the 



pans. 

 a, anterior retractor muscle; a, posterior retractor; t, lateral teeth; c, cardinal 

 tooth; /, lunale; «, umbo; A, hinge ligament; j. retractor of siphons;/, pallial 

 impression. 



