1909.] 



RECEXr BIOLOGY OF SOME LIVIXG SHELLS. 



755 



(text-figs. 236 ik 237) and M. truncata (text-figs. 238 & 239). 

 They dififer very obviously in external contour. The former is an 

 oval shell with its ends curved, one end being more obtuse than 



Text-fi^. 241. 



Text-fi?. 242. 



Text-fig. 241. — Hinge of Ilya arenaria. 



a, right valve ; h, left valve ; p, tip of diagonal keel. 



From A. S. Jeuseu, op. cit., by kind permission of the authoi-. 



Text-fig. 242. — Hinge of Mi/a truncata. 



c, locking-tooth; other letters as in text-fig. 241. 



From A. S. Jensen, op. cit., by kind permission of the author. 



Text-fis. 243. 



Hinge of Jifi/a truncata, var. ovata. 



Letters as in text-figs. 241 & 242. 



From A. S. Jensen, op. cit., by kind permission of the author. 



the other, while the other species has one end (that through 

 which the siphon of the mollusc is protruded and answering to 

 the more pointed end of the other species) sharply cut off, whence 

 Proc. Zool. Soc— 1909, Xo. LII. 52 



