58 INVERTEBRATA OF MASSACHUSETTS. 



The name and general shape of the English M. deaurata would 

 lead one to suppose it to be identical with our shell, and Mr. Conrad 

 has adopted that opinion. But Mr. Sowerby pronounces them not to be 

 the same. Indeed an examination of Turton's figure in his " British 

 Bivalves " would show his shell to be more closely allied to, if not 

 identical with, the next species. 



Mesode'sma Jaure'sii. 

 Shell ovate-triangular, thick, antiquated, coarsely ridged con- 

 centrically, inequilateral, lateral teeth very strong, curved, faintly 

 striated. 



, Figure 38. 



State Coll., No. 268. Soc. Cab., No. 2326. 



Mesodesma Jauresii, De Joannis ; Guirin, Mag. de ZooL, Oct. 1834. 



Shell ovate-triangular, thick and massive, surface rising into 

 ridges at the stages of growth, and covered by a coarse, dusky- 

 brown epidermis ; very inequilateral, behind short and regularly 

 rounded to the base, where there is an abrupt turn, and the basal 

 margin continues in nearly a straight line, or is a little arched ; 

 upper hinge margin also a straight line or slightly concave, ante- 

 riorly regularly rounded ; beaks scarcely rising at all, not in- 

 clined to either end ; the greatest diameter of the shell is midway 

 between the beaks and the anterior extremity. Spoon-shaped 

 cavity for the cartilage very deep ; on its anterior edge is the 

 vestige of a short, widely diverging V tooth, which will seldom be 

 found, as it is scarcely possible to open the valves without de- 

 stroying it. On each side is a very strong, curved, lateral tooth, 

 with a pit above it for the reception of the tooth in the opposite 

 valve ; the anterior tooth much longer than the posterior and 

 supported beneath by a thickening of the shell ; striae on the 

 teeth very faint. Within glossy white ; muscular impressions pro- 

 found, united by a simple palleal line, which has a small, semi- 

 circular sinus behind. Length 1| inch, height J^V inch, breadth 

 J-^ inches. 



Brought from St. George's and Grand Banks. I am not aware 

 that it has actually been found in the waters of this State. 



The obvious distinguishing marks between this shell and the preced- 

 ing are, in M. Jauresii the coarse, rough exterior, its longer and un- 



