302 PALAEONTOLOGY OF OHIO. 



GrEAMMYSIA ? RHOMBOIDES, Meek. 



Plate 16, figs. 7a, 5. 

 Orammysia rhomboides, Meek (1871); Proceed. Acad. Nat. Sci., Philad., XXIII., 72. 



Shell attaining a moderately large size, rhombic-suboval in outline, 

 with height equaling about three-fourths the length, not very convex, 

 the greatest convexity a little before and above the middle ; valves with- 

 out an oblique mesial ridge or fold, closed, or nearly so, all around; 

 basal margin most prominent just behind the middle, from near which 

 it ascends with a nearly straight outline obliquely forward, and more 

 abruptly with a convex outline behind; anterior side truncated oblique 

 forward from the beaks above, and very narrowly rounded near the mid- 

 dle; posterior side less narrowly rounded at the middle, with its upper 

 edge probably sometimes obliquely truncated; cardinal margin equaling 

 about one-third the length of the valves, and inflectea so as to form the 

 usual well-defined escutcheon, which narrows backward from the beaks ; 

 lunule rather deep, well defined, lance-ovate in form, and as long as the 

 truncated anterior dorsal slope ; beaks moderately prominent, not very 

 gibbous or very strongly incurved, and situated a little nearer the mid- 

 dle than the anterior margin ; posterior umbonal slopes forming a very 

 obscure rounded lidge, between which and the dorsal and posterior 

 dorsal margins there is a rather narrow, slightly concave, or flattened 

 space on each valve. Surface with only small marks or lines of growth, 

 which are gathered into very small obscure wrinkles along the margins 

 of the lunule. 



Length, 2.90 inches; height, measuring vertically from the most 

 prominent part of the base to the horizon of the tops of the beaks, 2.15 

 inches ; do., to cardinal margin behind the beaks, 1.93 inches ; convex- 

 ity, 1.40 inches. 



I only know this shell from cists which show neither the nature of the 

 hinge nor the muscular or pallial impressions. It presents no traces of 

 the characteristic oblique mesial fold or ridge seen in the typical forms 

 of Grammysia, and might, when its cardinal margin and lunule are con- 

 cealed in the matrix, be mistaken for a large Schizodus. Its well-defined 

 lunule and escutcheon, however, and obsolete muscular impressions, 

 show that it can not be even nearly related to that group. As the casts 

 show no indications of the characteristic internal cartilage process of 

 Edmondia, and it does not seem to have the habit of Cardiomorpha, I 

 know of no genus to which it appears to be more nearly related than to 



