332 



ZOOLOGY 



SECT. 



the hinge-line the inner, surface of the shell is produced into a pair 

 of massive, irregular hinge-teeth (f). On the inner surface of the 

 valve, towards its posterior end, are certain shallow depressions 

 marking the attachment of muscles (ad. ra, d. m). 



The dorsal valve (D) has no beak, but its posterior edge forms 

 a hinge-line which is produced in the middle into a strong cardinal 



d.m' 



FIG. 265. Magellania flavescens. A, the entire shell from the dorsal aspect ; B. from the 

 left side ; C, interior of ventral valve ; D, of dorsal valve ; ad. in. adductor impressions ; b. 

 beak ; c. p. cardinal process ; d. deltidium ; d. m. divaricator impressions ; d. r. dorsal valve ; /. 

 foramen ; p. m. protractor impressions ; s. tooth-socket ; s. L shelly loop ; up. septum : t. tooth ; 

 v. v. ventral valve. (After Davidson.) 



process (c. p) with a curiously folded surface : when the two valves 

 are in position this process fits between the hinge-teeth of the 

 ventral valve, the hinge-teeth in their turn being received into de- 

 pressions (s) placed on each side of the cardinal process. The inner 

 surface of the dorsal valve is produced into a median ridge or 

 septum (sp\ continuous posteriorly with the cardinal process, and 

 attached on either side of the base of the latter are the two ends 

 of a delicate calcareous ribbon, the shelly loop (s. I), which projects 



