Maryland Geological Survey 149 



margins, while tlie cardinal extremities are flattened; the cardinal area 

 is linear. Surface is marked by numerous closely arranged slender sub- 

 equal striae, -H-hich are bifurcated or increased by intercalation, and are 

 continued on the cardinal extremities to within a short distance of the 

 hinge-line; on an average specimen there are 12 striae in the space of 

 5 mm. The interior of the ventral valve shows diverging dental lamellae 

 and a narrow median ridge, while beyond the muscular and vascular 

 areas the surface is strongly pustulose in both valves. In some of the 

 Maryland specimens from the somewhat arenaceous shales, particularly 

 from McCoys Ferry, the internal impressions show the reverse of the above 

 characters in a median depression, diverging dental impressions, deeply 

 pitted surface outside of the vascular markings, and strongly striate 

 margin. 



This species occurs in abundance at McCoys Ferry largely in the form 

 of internal impressions which differ in no respect from New York speci- 

 mens found in similar deposits; the E. E. cut at 21st Bridge and Evitts 

 Creek below Wolfe Mill furnished specimens in which the shell is pre- 

 served ; while about 2 miles north of Hancock on the road from Hancock 

 to Harrisonville, Pa., specimens are common some of which are smaller 

 than the majority, show four or five cardinal spines and resemble figs. 

 10a and 10& on pi. xxi, vol. iv, Palaeontology of New York. There is 

 apparently no difference in characters between the Maryland specimens 

 and the several forais of the species found in New York. It is readily 

 distinguished by its large size, convex ventral valve with the frequent 

 shallow sinus, numerous closely arranged surface striae, while the pus- 

 tules and striae are characteristic of the outer portion of the inside of 

 the valves or internal impressions. 



Length, 10-20 mm. ; width, 13-28 mm. 



Occurrence. — Eomney Formation, Hamilton Member. Williams 

 Eoad, 3^ miles southeast of Cumberland; east bank Evitts Creek below 

 Wolfe Mill; Williams Eoad, ^ mile east of Queen City Hotel, Cumber- 

 land; in Jennings Eun, ^ mile west of Corriganville ; B. & 0. E. E. cut 

 at 21st Bridge; on National Eoad, \ mile west of Tonoloway Eidge; on 

 the Hancock-Harrisonville Eoad about 2 miles north of Hancock ; 



