«44 PALJJONTOLOGY OF NEW- YORK. 



Eatonia peculiaiis. 



Plate XXXVIII. Fio. 21-26; and Plate CI. Fio. 2. 

 Jttrypa ptculxarU : Conbad, Ann. Report on the Palaoontology 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 roimded mesial fold, which becomes very pro- 

 minent in front : margins of the valves denticulate. 

 Surface marked by fine radiating bifurcating strise ; 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 diiTcrs 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 and profile views. 

 Fig. 23 a, b. Dorsal and front views of a full-grown specimen, showing the denticulations 



in front. 

 Fig. 24 a, b, c. Profile, ventral, and front views of a specimen which shows more distinctly 



the denticulations in front. 

 Pig. 25 a, b. Ventral and dorsal views of a cast of this species. 

 Fig. 26. Enlargement of the surface strise. 



