MARYLAND GEOLOGICAL SURVEY 245 



terior side; brachial processes slender, prominent, and directed obliquely 

 forward ; surface granular and showing the radiating striae. 



" Ventral valve convex, with elevated mesial ridge, greatest convexity 

 just behind the middle; beak arched,. projecting slightly; area moderate, 

 narrowing laterally; foramen an equilateral triangle, partly occupied by 

 the cardinal process of the other valve. Interior strongly concave, show- 

 ing moderately prominent teeth ; dental laminae extend from the base of 

 the teeth forward, gradually becoming more indistinct as they fade away 

 in a circular line to the mesial depression, forming a heart-shaped cavity 

 for the muscular scars; surface granular and showing the radiating 

 striae. 



" Surface of both valves ornamented by fine radiating striae, that 

 increase by bifurcation ; lateral striae curved so that a few of them run 

 out on the hinge line; concentric striae plainly visible with the aid of a 

 magnifier, and sometimes visible to the unaided eye; imbricating marks 

 of growth usual. Length of an average full-grown specimen, 0.50 inch; 

 breadth, 0.58 inch; convexity, 0.20 inch. They vary, however, from one- 

 fourth this size to one-half larger." Miller, 1875. 



This is probably the most abundant fossil of the Eden shale wherever 

 exposed. In the Appalachian Valley of Pennsylvania and Maryland it 

 occurs in the upper sandy layers of the Martinsburg. 



Occurrence. MARTINSBURG SHALE (Eden division). Jordans Knob, 

 one and one-half miles northeast of Fort Loudon, in Pennsylvania, and the 

 west slope of Eickard Mountain in Maryland furnish specimens. 



Collections. Maryland Geological Survey, U. S. National Museum. 



DALMANELLA ELECTRA (Billings) 



Plate XXXV, Fig. 6 



Orthis electro, Billings, 1865, Pal. Foss., vol. i, p. 79, fig. 72. 

 Dalmanella electro, Weller, 1903, Geol. Surv. New Jersey, Pal., vol. iii, p. 125, 

 pi. iv, fig. 13. 



Description. Shell wider than long, the usual dimensions being about 

 6 mm. in length and 7 mm. in width, with the hinge-line a little shorter 

 than the greatest width, and the cardinal extremities angular. Pedicle 



