Y2 PROCEEDINGS OF THE ACADEMY OF 



GRAMMYSIA'? RHOMBOIDES, Meek. 



Shell attaining a nioderatel}' large size, not very convex, the 

 greatest convexity a little before and above the middle ; valves 

 witliout an oblique mesial ridge or fold ; rhombic suboval in out- 

 line, with height equalling about three-fourths the length, closed 

 or nearly so all around ; basal margin most prominent just behind 

 the middle, from near which it ascends with a nearly straight out- 

 line obliquely forward, and more abruptly with a convex outline 

 behind ; anterior side truncated obliquely forward from the beaks 

 above, and ver}^ narrowdy rounded near the middle ; posterior side 

 less narrowly rounded at the middle, with its npper edge probabl}^ 

 sometimes obliquely truncated ; cardinal margin equalling about 

 one-third the length of the valves, and inflected so as to form a well- 

 defined escutcheon that narrows backward fi'om 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 middle than the anterior margin ; posterior umbonal 

 slopes forming a very obscure rounded ridge, 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 ver}'- 

 small obscure wrinkles along the margins of the lunule. 



Length, 2.90 inches ; height, measuring verticallj^ from the 

 most prominent part of the beaks to the horizon of the tops of 

 the beaks, 2.15 inches; do. to cardinal margin behind the beaks, 

 1.93 inches ; convexity, 1.40 inches. 



I only know this shell from casts, 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 cardi- 

 nal margin and lunule are concealed in the matrix, be mistaken 

 for a large Schizodus. Its well-defined lunule and escutcheon, 

 however, and obsolete muscular impressions, show that it cannot 

 be even nearly related to that group. As the casts show no indi- 

 cations of the characteristic internal cartilage process of Eclmon- 

 dia, 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 Grammysia, and have concluded to place it provisionally 



[June 6, 



