Wappinger Valley Limestones. 145 



valves are covered with well-defined scattered tubercles, corres- 

 ponding apparently with the scattered pits of the external 

 surface. 



No eye-tubercle nor muscle-spot is visible. Further particu- 

 lars, as to relative obliquity of the dorsal angles, etc., cannot 

 be ascertained until more perfect specimens are collected. In 

 specimen No. 1'75, the valve appears to be a little wider on the 

 left-hand than on the right-hand ; it is therefore probable that 

 the specimen is the right valve. 



Found chiefly in the calcareous shale, but occasionally in the 

 compact limestone. Some surfaces of the shale are black with 

 its fragments, but owing to its brittleness no perfect specimens 

 has been yet obtained. 



Kutorgina Stissiugensis, n. sp. Plate VI, figs. 5, 6, 7 and 8. 



Shell black, phosphatic, slightly transverse ; width about 

 three-tenths greater than the length. Those collected from the 

 limestone are about eight millimeters in width ; specimens 

 found in the calcareous shale are sometimes from eleven to 

 twelve millimeters wide or even more. General shape, semi- 

 circular. 



The cardinal margin slopes forward somewhat on each side 

 of the beak, and makes obtuse angles with the lateral margins, 

 on account of the incurving of the latter. It is shorter than 

 the greatest width of the shell which is along a transverse line 

 one-third of the distance from the beak to the front. Hinge- 

 line not evident, but apparently a little curved. 



The ventral valve has the beak elevated, pointed, and pro- 

 jecting somewhat behind the cardinal margin. From the beak 

 the surface slopes down toward each lateral margin, and to the 

 front margin, becoming sometimes slightly concave at the 

 central portions of the shell. Along the cardinal border the 

 shell is suddenly deflexed, making a distinct false area which, 

 however, is separated into two parts by a vacant deltidial space 

 under the beak. As the surface of this false area is exfoliated 

 in specimens observed, it cannot be positively determined 

 whether the surface ornamentation of the valve is extended 

 over it. The edge between the false area and the upper sur- 

 face of the valve is not sharp, but gently rounded. 



The dorsal valve is depressed and nearly flat, beak low ; 

 otherwise resembles the ventral valve, except that in specimens 

 collected it appears a little more transverse. 



The surfaces of both valves are covered with very fine, sharp, 

 concentric ridges, traversed by strise scarcely visible to the 

 naked eye. Under a strong triplet these strise prove to be very 

 delicate longitudinal undulations radiating from the beak. 



