MOLLUSCA. 605 



1 86 1. Dosinia haddonfieldensis Lea, Proc. Acad. Nat. Sci. Phil. 



(1861), p. 149. 

 1867. Cyprimeria cretacensis Con.., Am. Jour. Conch., vol. 3, 



p. 9. 

 1869. Cyprimeria cretacea Con., Am. Jour. Conch., vol. 5, p. 



98, pi. 9, fig. 12. 



Description. Shell in the larger specimens attains a length 

 of over 50 mm., and a height of over 40 mm. The proportion 

 of height to length in eight individuals varies from I : 1.24 

 (1.18) to i : 1.39 (1.31), the average proportion of the eight 

 individuals being i : 1.29-)- (1.22-)-). The specimens being 

 internal casts the height is less than that of the actual shells, 

 and the numbers given in parenthesis above indicate the pro- 

 portions when allowance has been made for this increased height 

 of the actual shells. The proportions in parenthesis, therefore, in- 

 dicate more nearly the actual proportions of the species. A 

 plaster cast taken from a natural mould and therefore showing 

 the actual form of the shell, has a length of 46 mm., with a 

 height of 37.5 mm., the proportions of height to length being" 

 as i : 1.23-. The position of the beak in the same eight indi- 

 viduals vary from .32 to .45 of the length of the shell from the 

 anterior extremity, the average position being .36+- 



The anterior margin of the shell is broadly rounded, passing 

 into the broadly rounded basal margin; posteriorly the basal 

 margin curves upward and passes into the subtruncate pos- 

 terior margin with an obtusely subangular bend; the middle of 

 the subtruncate posterior margin is at about the mid-height of 

 the shell, and its direction is nearly at right angles to the greatest 

 length of the shell. Above the subtruncate posterior margin is 

 an obtusely subangular bend beyond which the post-cardinal 

 margin describes a steadily increasing curve to the beaks. Valves 

 depressed convex. 



The surface of the valves towards the umbo is marked by 

 fine, regular, rounded, concentric costse, for a distance of 10 

 millimeters, more or less from the beak, four or five of these 

 costae occupying the space of one millimeter. Beyond the um- 



