440 PALAEONTOLOGY OF NEW-TORK. 



Rliyiii'liuiu'lla iiiultistiiata. 



Plate CII. Fig. 3; and Plate CVI. Fig. 3. 

 KhyndtoneUa muitUtriata : Hall, Regents' Report for 1856, p. 85; Palaeozoic Fossils, 1857, p. 45. 



Shell depressed suborbicular. Ventral valve depressed convex, most ele- 

 vated in the umbonial region, flattened towards the lateral margins 

 and depressed in front, forming a broad shallow undefined sinus. 

 Dorsal valve unknown. 



Surface marked by numerous fine regular bifurcating striae, which are 

 well defined nearly to the apex of the beak. 



This species is more finely striated than the preceding, and is more nearly circular 

 in form, the length and breadth being about equal; while in the casts of that one, 

 the width is greater than the length. 



Plate cii, fig. 3. View of the dorsal valve. 



Plate cvi, fig. 3. An imperfect dorsal valve of a younger specimen. 



Geological position and locality. In the Oriskany sandstone : Helderberg moun- 

 tains. 



Rliynciioiiella pleiopleura. 



Plate CII. Fig. 3 a- c & 4 a - c. 



Alrypa pletopUura : CoNRAD, Annual Report on the Paljeontology of New- York, p. 55. 

 Rkifnchondla pltiopUwa : Hall, Regents' Report for 1856, p. 86; Palaeozoic Fossils, 1857, p. 46. 



Shell transversely oval. Dorsal valve the larger, somewhat gibbous, 

 having a round undefined mesial fold : beak incurved ; cardinal border 

 excavated in deep fossets on each side of the beak, for the reception 

 of the dental lamellae of the opposite valve. Ventral valve nearly flat, 

 most elevated near the beak, having a somewhat deep broad rounded 

 sinus near the front margin, which is prolonged into a rounded or 

 subtriangular projection. 



Sueface ornamented by from sixty-four to seventy subangular bifurcating 

 striae or plications. 



