NATURAL SCIENCES OF PHILADELPHIA. 13Y 



break in one valve by repeated blows with the beak — a tedious 

 process, it seemed, in some cases that I watched. The fracture 

 of this shell is clean, sharp, and almost vitreous. 



Dosinia discus, Reeve. {Artemis concentrica, Born.) 



Very abundant ; the dead ones, almost always with the hinge 

 intact, are conspicuous on the beach ; and some live specimens 

 were procured about the harbor. 



Lucinopsis, sp. indet. 



Dredged. 

 Petricola pholadiformis, Lam. 



Dead shells are common ever^'where, but especially on the 

 beach. 



Raeta canaliculata, Say. 

 Beach, very abundant. 



Eaeta lineata, Say. 



Not ordinarily common ; but occasionall}^, after storms that 

 seem to disturb some special situations they inhabit, they are 

 strewn on the beach in large numbers. 



Mactra raveneli, Conr. 



Strewn in profusion on the beach and elsewhere. Most of the 

 worn specimens are variously discolored. 



" Probably what is catalogued as M. oblonga, Say, by Kurtz 

 and Stimpson." 



Mactra similis, Say. 



With the last ; not so common. 



" I find among the specimens some that I think are this, but it 

 is a doubtful species." 



Mactra lateralis, Say. 



Abundant, with the first. 



Donaz variabilis. Say. 



Very abundant ; living a few inches below the surface of the 

 sand, chiefly of the beach itself. At certain states of the tide, &c., 

 they are in the habit of coming to the surface, and of disporting 

 with considerable agility. They must, however, be somewhat 

 cautiously watched, as they have a sense of observation, whatever 

 it may be, that imforms them of probable danger, and causes them. 



1871.] PART II.— 10 



