Weno and Pawpaw Formations 135 



DESCRIPTION: Shell subovate, inequilateral, subequivalve, beaks 

 pointed anteriorly (prosogyrate) ; surfaces of both valves covered with 

 numerous, simple, fine, striaeiform, concentric growth lines, and having a 

 few widely spaced, coarser growth rings. Shell preserved, interior filled 

 with ironstone. The beaks are inconspicuous, recurved anteriorly forming 

 anterior to them a small notch in the margin and are rounded, incurved 

 and approximate ; anterior to them the margins of the valves are in contact 

 and the growth lines are imbricated and separated, making several lines 

 parallel to the margins of the valves. Posterior to the beaks is a much 

 wider triangular depression between the margins of the valve. It runs 

 from the umbo backwards to the postero-dorsal, angle; its bottom is the 

 apposed inner dorsal margins of the valves, its top the separated outer 

 dorsal margins, while its sides consist of growth lamellae terminating 

 abruptly and together constituting the thickness of the valves at this 

 point. The groove in one individual contains over the medial half of its 

 length a well preserved external hinge ligament. This has a chitinous 

 appearance but is replaced by calcareous material. 



The dentition is approximately that of Cyprimeria Conrad. The hinge 

 of the left valve consists of two posterior lamellae, two teeth and an an- 

 terior lamella. The most dorsal posterior lamella is very broad and ob- 

 lique, and is nearly parallel to the inner dorsal shell margin, which it has 

 overgrown. It is roughly lanceolate or blade-shaped, the point being di- 

 rected toward the umbo, the curved back directed ventrally, the edge di- 

 rected dorsally and a narrowed portion directed postero-dorsally. It is 

 separated by a narrow groove from the shorter second posterior lamella, 

 which lies parallel to it and is coalescent with its umbonal half. Ventral 

 to this lamella there is a narrow, deep, elongated pit, which separates it 

 from the more posterior tooth. This pit in one individual contains a mass 

 of brownish material chitinous in appearance but in fact calcareous. The 

 two teeth are sharp, ridge-like and elongated, making an angle of about 

 60 degrees with each other; they are remote and are separated by a tri- 

 angular area, raised centrally. Running anteriorly from the base of the 

 tooth is an elongate elevated margin which may be taken as an anterior 

 lamella. Dorsal and parallel to this is an elongate groove which is bounded 

 dorsally by the upturned inner dorsal edge of the valve. Parallel and an- 

 terior to the anterior tooth is a narrow deeper depression the length of the 

 tooth, which anteriorly connects with the groove. Below the teeth is an 

 elongated area of small pits and punctations on the dorsal portion of the 

 inner surface of each valve. Cyprimeria crassa Meek has been recorded 1 



'Hill, Annotated Check List, p. 14. 



