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PALAEONTOLOGY OP 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 c. An individual more extended on the beak than usual. 
Fig. 1 h - o. 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 eminens (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, iu the much greater 
prominence of the mesial fold in front, and the broader plications. It also presents 
notable differences in the characters of the internal impressions. 
Fig. 2 a. Dorsal valve of the cast. 
Fig. 2 b. 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. •-* 
