420 PALEONTOLOGY OF NEW YOKK. 



Centroiiella liecate. 



PLATE LXI A, FIGS. 27-29. 

 Centrmtlla hecate: Biilinos. Canadian Journal, May, 1861, page 272. 



Shell elongate, half as long again as wide, with a slightly incurved project- 

 ing ventral beak. 



Dorsal valve regularly arcuate from beak to base, with a moderate mesial 

 sinus, which is angular in the bottom. 



Ventral valve sharply angular or carinate along the middle, with flattened 

 sides. 

 This species resembles 0. alveata in form, but is much smaller, the sinus is less 



deep and the cardinal margins not rejlected while the lateral mai-gins of the beak 



are rounded instead of being sharply angular. 



Geological foitnation and locality. In the Upper Helderberg limestones at 



Cayuga, C. W.~ 



Meristella lenta (n. s.). 



PLATE LXIII, FIGS. 19-22. 



Shell small, broadly ovate, or transversely oval, with a slightly projecting 



beak and very unequally convex valves. 

 Ventral valve nearly flat in the upper part, with sharply angular cardinal 



margins becoming deeply and subangularly sinuate towards the front, 



where it is slightly bent upwards. 

 Dorsal valve very ventricose in the umbonal portion, and subangular along 



the centre, with the sides somewhat flattened. 



This species differs from any described form of the genus so far as it can be 

 ascertained. In the form of the ventral valve it approaches somewhat the M. 

 {Pentagonia) unisulcata, but the sinus is narrow instead of embracing the greater 

 part of the valve, and it differs so materially in other respects that there is no dan- 

 ger of confounding the two. 



Geological for motion and locality. In rocks of the age of the Oriskauy sand- 

 stone or Upper Helderberg limestones, near Cayuga, C. W. 



