702 SYSTEMATIC PALEONTOLOGY 



in front; beaks broad, rather strongly elevated above the hinge line, 

 nearly central in position and directed anteriorly. Hinge line nearly 

 straight, the anterior and posterior portions sloping very gently on each 

 side of the beak ; antero-cardinal margin concave ; anterior margin round- 

 ing from the cardinal into the basal margin ; basal margin nearly straight 

 or slightly convex in the middle, curving upward a little more abruptly in 

 front than behind ; postero-basal extremity rounded ; posterior margin 

 nearly vertically truncate; post-cardinal extremity obtusely subangular; 

 post-cardinal margin straight. Valves moderately convex, with an 

 obscure, rounded, umbonal .ridge along both the anterior and posterior 

 umbonal slopes ; the cardinal margins inflected both in front of and behind 

 the beaks. Surface of both valves in the casts marked by rather fine, more 

 or less irregular, concentric lines of growth. 



" This shell, in its general outline, somewhat resembles Periplomya 

 elliptica, but with the extremities of the shell reversed, the anterior, 

 extremity of that species being the broader and the beak being directed 

 backward. In Solyma lineolaia, however, the posterior margin is truncate 

 while the anterior margin of P. elliptica is rounded, and the anterior 

 extremity is much broader than the posterior extremity of that shell. 

 The two more or less obscure umbonal ridges are also a distinguishing 

 mark of this species, but these ridges have been made too conspicuous in 

 Whitfield's illustration of the species. Upon one of the internal casts of 

 this species which has come under observation, there seems to be an impres- 

 sion of a very deep pallial sinus extending forward to the center of the 

 shell." Weller, 1907. 



Ligament, as implied by Conrad's figure, external, opisthodetic, seated 

 upon a marginal nymph, armature of right valve consisting of two slender 

 laminar teeth, diverging at a small angle from beneath the umbone. 



Eepresented in Maryland by a single imperfect cast. 



Occurrence. MAGOTHY FORMATION. Good Hope Hill, District of 

 Columbia. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Xatural Sciences, Xew Jersey Geological Survey, U. S. National Museum. 



