a«a PALAEONTOLOGY OF NEW- YORK. 



Kig. 4 t, f, g, h. Views of a specimen of extremely large size, showing the broad and shal- 

 low mesial sinus, and the linguiform extension in front, which is bent abruptly 

 upwards. 



Fig. 5 o, b, e, d. Views of a specimen having the form of the two preceding, but with a 

 more narrow and angular sinus. 



Geological position and locality. In the Upper Pentamerus limestone, and, rarely, 



in the Shaly limestone of the Lower Helderberg group : Helderberg mountains ; 



Schoharie, and Carlisle. 



Merista meeki( n. s.). 



Plate XLIV. Fig. 6 a - rf. 



Shell cordate ovate, very gibbous, sloping from below the middle towards 

 the beaks at an angle of about 80°. Ventral valve profoundly arcuate 

 from the beak to the anterior margin, where it terminates in a promi- 

 nent abruptly tapering mesial prolongation, having a broad angular 

 sinus extending from near the beak to the base of the shell : beak 

 flattened on the outside, subangular on.its lateral slopes, closely in- 

 curved upon that of the opposite valve. Dorsal valve elevated along 

 the middle, sloping laterally with an abrupt curve, very gibbous in the 

 umbonial region : beak incurved. 



Surface smooth, or marked by faint concentric lines of growth. 



The shorter and more globose form of this species, as well as the deep angular 



sinus and flattened umbo of its ventral valve, are sufficient to distinguish it from 



all the preceding species. 



Fig. 6 a, h. Ventral and dorsal views of this species. 

 Fig. 6 c, d. Profile and front views of the same. 



Geological position and locality. In limestone of the age of the Lower Helderberg 

 group : Tennessee. 



McriStJil ( species undetermined ). 



Plate XLV. Fio. 1 a, 6, c, d. 



ThtS species, of the size of fig. 1 o and more rarely of figs. 1 6, c, occurs in con- 

 siderable numbers in the Upper Pentamerus limestone. Fig. 1 d has the same form 

 and proportions ; but I have been unable to obtain such a series of specimens as 

 would enable me to determine fully its relations to the other species described, or 

 whether it may be the extreme young of M. princeps. 



