244 
PALAEONTOLOGY OF NEW-YORK. 
Eatonia peculiaris. 
Plate XXXYIII. Fig. 21-26; and Plate Cl. Fig. 2. 
Atrypa peculiaris : Conrad, Ann. Report on the Palaeontology of New-York, 1841, p. 56. 
Shell longitudinally ovate, the proportion of length and breadth variable: 
cardinal margins sloping abruptly from the beaks. Ventral valve de¬ 
pressed convex in the middle towards the beak, and flattened towards 
the margins, which are abruptly inflected along the cardinal slopes; 
below the middle, extended in a broad not strongly defined mesial 
depression, which is prolonged in front into a linguiform extension : 
beak moderately elevated, perforate. Dorsal valve convex in the middle, 
and sloping abruptly to the lateral margins; the central part below the 
middle elevated into a rounded mesial fold, which becomes very pro¬ 
minent in front ; margins of the valves denticulate. 
Surface marked by fine radiating bifurcating strife; a stronger elevated 
one along the centre of the mesial sinus, and a narrow longitudinal 
depression down the centre of the dorsal valve, the mesial elevation 
of which is sometimes obtusely subplicate near the margin. 
This species was regarded by Mr. Conrad as restricted to the Oriskany sandstone; 
but in the course of many years’ collections, a considerable number of specimens 
have been found in the limestone of the Lower Helderberg group. In its surface 
characters, it scarcely differs from the preceding species : the form, however, is 
always more or less distinctly ovate, the mesial sinus less deeply and less distinctly 
pronounced; while the mesial fold of the opposite valve is less abrupt, and does 
not extend so nearly to the beak of the valve; the margins of the valves, and 
particularly of the ventral valve, are distinctly inflected along the cardinal slopes, 
giving an undefined oval area on each side below the beaks. The crenulations in 
front are always visible in well-preserved specimens, and these sometimes produce 
a slight undulation or plication of the exterior near the margins. 
Fig. 21. Illustrations of one of the shorter forms of this species. 
Fig. 22 a, b. Dorsal ancl profile views. 
Fig. 23 a, b. Dorsal and front views of a full-grown specimen, showing the dentieulations 
in front. 
Fig. 24 a, b, c. Profile, ventral, and front views of a specimen which shows more distinctly 
the dentieulations in front. 
Fig. 25 a, b. Ventral and dorsal views of a cast of this species. 
Fig. 26. Enlargement of the surface striae. 
