42© 
PALEONTOLOGY OF NEW YORK. 
Centroiiella hecate. 
PLATE LXI A, FIGS. 27-29. 
Centronella hecate: Billings. 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 C. alveata in form, but is much smaller, the sinus is less 
deep and the cardinal margins not reflected while the lateral margins of the beak* 
are rounded instead of being sharply angular. 
Geological formation and locality. In the Upper Helderberg limestones at 
Cayuga, C. W. 
Meristella lenta (n. s.). 
PLATE LXHI, 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 formation and locality. In rocks of the age of the Oriskany sand¬ 
stone or Upper Helderberg limestones, near Cayuga, C. W. 
