"*'i« PALAEONTOLOGY OF NEW-YORK. 



surface; while in E. sinuata and E. eminens, the specimens yet seen are too imperfect 

 to determine whether this character originally existed or not. 



Fig. 1 a, b. Individuals in which the plications are more numerous than ordinary. 



Fig. 1 c, d, f, g. Individuals in which the plications are much subdued, and in 1 c, d, are 

 scarcely marked. 



Fig. 1 e. An individual more extended on the beak than ustial. 



Fig. 1 h - 0. Individuals presenting the usual varieties of form and surface of this species. 



[ Fig. 1 o preserves the fine longitudinal striae.] 



Fig. 1 p, r, s. Ventral, front, and cardinal views of an unusually large individual, the valves 

 of which are slightly opened. 



Fig. 1 t, u. Ventral and dorsal views of the cast of a small individual. 



Fig. 1 X, y. Casts of the ventral valve. 



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

 group : Helderberg mountains; Schoharie, Carlisle, Hudson, Catskill, and other 

 places. 



Eatonia cminens (n.s.). 



Plate XXXVII. Fig. 2 a, b, c. 



Shell somewhat depressed globose or subquadrilateral, deeply sinuate and 

 abruptly elevated in front. Ventral valve sloping from the beak and 

 sides into a broad undefined sinus, and abruptly extended in front with 

 a regular curve into a -large subtriangular prolongation, which lies 

 nearly at right angles to the plane of the valve near the beak. Dorsal 

 valve much the larger, extremely elevated in front, and declining 

 abruptly towards the beak and sides : mesial elevation with four plica- 

 tions, the two middle ones much more prominent. 



Surface of the cast marked by fourteen subangular plications ; those of 

 the mesial elevation more angular than those on the sides. 



This species differs from E. medialis, to which it is related, in the much greater 

 prominence of the mesial fold in front, and the broader plications. It also presents 

 notable difiFerences in the characters of the internal impressions. 



Fig. 2 a. Dorsal valve of the cast. 



Fig. 2 6. Ventral view of the same. 



Fig. 2 c. Profile view, showing the great elevation of the dorsal valve. 



Geological position and locality. In shaly limestone of the age of the Lower Hel- 

 derberg group : Tennessee. 



