TRENTON CONGLOMERATE OF RYSEDORPH HILL 79 



ventral margin more gently rounded. Body of valve 

 moderately to strongly convex, highest in the central 

 region, from which it slopes equally to all sides. The largest 

 of the figured specimens, which is slightly exfoliated, shows an 

 apical muscle impression; another an elongate prominence, 

 situated nearer to the cardinal line, evidently the filling of a 

 muscle impression; while a third specimen (pi. 5, fig. 2) which 

 has the crust preserved, shows an elongate kidney-shaped apical 

 impression, which is evidently the last trace of the sulcus. 

 Marginal area not concave and curved outward as in the other 

 species, but more or less convex and curving inward, becoming 

 wider toward the ventral region, and provided with strong radiat- 

 ing ribs, which in some specimens are partly composed of gran- 

 ules. Surface very faintly granulose. 



Dimensions. Length 2.1 mm; hight 1.6 mm; thickness .6 mm. 



Horizon and locality. Gray crystalline limestone pebbles of 

 Rysedorph hill conglomerate. (Group 7) 



Observations. This interesting form can be compared only with 

 Eurychilina aequalis, from the Ghazy and Lowville 

 limestone (Stones river group) of Kentucky, 1 from which it seems 

 to differ only in not possessing a distinct sulcus, and in having 

 the marginal area strongly ribbed. 



Eurychilina objiqna sp. nov. 

 PL 5, fig. 10-12 

 There have been found in the gray limestone several large 

 specimens of Eurychilina which are nearly related to E. d i a n - 

 thus, but differ uniformly in certain important features. 

 These are the more elongate form of the semi-elliptic valve, the 

 greater convexity of the body of the valve, and the situation 

 of the apex of the convexity in the posterior half, whence the 

 valve evenly slopes anteriorly, the entire absence of any trace 

 of an apical sulcate impression, and the considerably greater 

 width of the marginal convex area, which soon reaches its full 



1 Cin. soc. uat.hist. Jour. 1890-91. 13:129. 



