,332 



ZOOLOGY 



SECT. 



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

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

 valve, towards its posterior end, are certain shallow depressions 

 marking the attachment of muscles (ad. m, 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 



B 



Fia. 205. Magellania fiavescens. A, the entire shell from the dorsal aspect ; B. from the 

 leftside; C, interior of ventral valve ; D, of dorsal valve; ml. m. adductor impressions; b. 

 beak ; r. />. cardinal process ; d. deltidium ; <?. M. divaricator impressions ; d. r. dorsal valve ; /. 

 foramen ; /. m. protractor impressions ; s. tooth-socket ; x. 1. shelly loop ; sji. septum : t. tooth ; 

 /. .-. 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 



