180 PALEONTOLOGY OF NEW YORK. 



sitic in its habit, attachment being considerably aided by the overlapping 

 margin of the upper valve. Length and width of an average adult ; upper 

 valve, 9 mm., lower valve, 7.5 mm. 



Lower Helderberg group. Near Clarksville, N. Y. 



Crania agaricina, sp. nov. 



PLATE IVh.^FIG. 2. 



Shell small. Apex posterior, slightly elevated. Surface covered by a few 

 coarse, elevated, radiating lines, of which about twelve reach the apex. 

 These increase by intercalation toward the margin, to about thirty. The 

 edges of these ridges appear to be minutely granulose. Length of the orig- 

 inal specimen (allowing for its incurvature upon the surface of attachment), 

 5 mm. 



Lower Helderberg group. Near Clarksville, N. Y. 



Crania pulchella, sp. nov. 



PLATE IV H, FIG. 3. 



Shell like that of C. agaricina, but larger and with much finer, more numerous 

 radiating ribs. These are about sixty in number at the margin of the valve. 

 Length of the original specimen, 8 ram. 



Lower Helderberg group. Near Clarksville, N. Y. 



Crania qranosa, sp. nov, 



PLATE IV H, FIGS. 19, 20. 



The original specimen is an upper valve, quite irregular iu its growth, with 

 a nearly central beak and strong convexity. The surface is completely covered 

 with closely set granules which are somewhat coarser toward the margins A 

 few concentric wrinkles of growth are also visible. Diameter, 18 mm. 



Hamilton group. Centerfield, N. Y. 



