I. AMPHINEURA. 35 i 



mantle extends beyond the shell and is covered with spines, while 

 in the mantle cavity beneath are, right and left, a series of ctenidia. 

 Xerves enter the shell and end with noticeable sense organs (ajs- 



FlG. 344— C/iifon SQurir))0.si(s, dorsal view. (After Haller.) .4, the entire animal; /?, 

 after removal of shell and viseera. a, anus; C, brain; K, ctenidia; o, mouth; 

 /', xjedal nerve cord; pi, pleurovisceral nerve cord. 



thetes and, in some, eyes, fig. 345). The symmetry of the Ijody is 

 also expressed in the viscera. The aims is medial, and right and 



Pm ;i4.-, _Eye and a?sthetes „t Ai:m,lhnplrnf(t xpiniui-r. (After :Mo3eley.) «, macraE-s- 

 thete; 'i, micra-sthete; f. calcareous cornea; ;;, lens; li, iris; t, pigmented cap- 

 sule; H, jJ, nerves; ?', retina. 



left of it are the openings of the nephridia and sexual organs. The 

 sexes are separate, the gonads unpaired, while corresponding to the 

 paired arrangement of the gills there are two auricles to the heart. 



Tho Cliitoiis are represented on our northeastern coast by several 

 sir.all species {Trachydennon* Ainkula*)\ farther south and on the 

 Paciflc shores are larger species {CryptocJiitoti *). 



