ORISKANY SANDSTONE. 44a» 



extending from beneath the thickened cardinal process for one-third the 

 length of the shell. The crural processes are comparatively long and 

 slender, and, at their base, are separated by a prominent callosity. In 

 older shells this callosity becomes thickened and duplicated; and the 

 median groove in the cardinal process at the base of the crura, lying 

 below the plane of the beak, becomes filled up, and the process extended 

 above the beak, with an oval impression on each side. 



This beautiful shell is remarkable for its regular ovoid form and vertically 

 compressed sides. It diifers from any other species of equal size known to me, by 

 the entire absence of a sinus in either valve. Adult specimens appear to have been 

 generally higher than wide, though in younger individuals the width is greater 

 than the height. 



Fig. 1 a. Dorsal view of a specimen of medium size. 



Fig. 1 6. Profile of tlie same, showing some parasitic bodies attached at the front and sides. 



Fig. 2 a. Dorsal view of a larger individual. 



Fig. 2 ft & c. Profile and front views of the same. 



Fig. 2 rf. Cardinal view, showing the deep sinuosities in the dorsal valve and the auricular 



extensions of the ventral valve. 

 Fig. 3. A partial cast of a large individual of this species. 



Fig. 4 a. The ventral valve, showing the muscular impression : the teeth are broken oflF. 

 Fig. 4 6. A fragment of a dorsal valve, showing the muscular impression, teeth, etc. 

 Fig. 4 c. Cardinal view of the preceding specimen. 



Fig. 5. The rostral portion of a specimen, showing the junction of the two valves, the median 

 septum in the dorsal valve, and the crural processes of the ventral valve. 



Fig. 6 a. The interior of the dorsal valve, showing the median septum, the crural processes, 

 the thiclcened cardinal process with the prominent bilobed summit, and the dental 

 fossets. 



Fig. 6 6. Cardinal view of the preceding specimen, showing the sinuosities on each side of 

 the bealc, the cardinal and crural processes. 



Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 



