376 The Ohio Journal of Science [Vol. XIX, No. 7, 



The pedicel valves are distinctly concave, the beak being slightly 

 elevated above the adjacent parts of the valve. The brachial valve is 

 convex, with the greatest convexity anterior to the center of the valve. 

 The sides of the shell converge moderately posteriorly, so that the 

 hinge-line is shorter than the greatest width of the shell, but there is no 

 conspicuous rounding of the postero-lateral angles. Contrasted with 

 Schuchertella tenuis, the shell is much more elongate, but the amount of 

 elongation varies considerably in different individuals. While in the 

 more moderately elongated shells the anterior outline may be broadly 

 and regularly convex, in the more strongly elongated shells the convexity 

 of the anterior outline increases toward the median line, producing 

 soinetimes a subtriangular appearance. Associated with this sub- 

 triangular appearance the concavity of the pedicel valve is most pro- 

 nounced along the median line, and there is a corresponding accentuation 

 of the convexity of the brachial valve, especially anteriorly. In the 

 most elongated specimen at hand the greatest width of the shell was near 

 the hinge-line, and equalled 50 millimeters; at mid-length, the width 

 equalled 46 millimeters; ten millimeters from the front the width 

 equalled 34 millimeters; the entire length of the shell was 50 milli- 

 meters. By comparing these dimensions with those indicated by 

 Figures lA and IB on the accompanying plate, the amount of divergence 

 of this outline from the normal type may be noted. It is in these more 

 elongate shells that the concavity of the pedicel valve is most pronounced 

 reaching in one case 6 millimeters. The greatest convexity noted so 

 far is that shown by the specimen represented by Figures lA and IC, 

 on Plate XVI; in this case it equals 16 millimeters, while in other 

 specimens of equal length the convexity may not exceed 9 millimeters. 

 The radiating striae tend to be subequal in size, excepting of course at 

 their point of insertion. They vary in number from 7 to 10 in a width 

 of 5 millimeters. 



The interior of the pedicel valve is exposed frequently, but the 

 clearest indications of the outlines of the muscular area are presented 

 by the casts presented by the matrix filling these interiors. In outline 

 this muscular area is almost circular and is distinctly delimited except 

 near the median line anteriorly. Posterior to the center of this muscular 

 area there is a small oblong space locating the position of the posterior 

 adductors. A median line of elevation, often bordered laterally by 

 shallow lines of depression, extends across this oblong space. In 

 occasional specimens the remainder of the muscular area is marked by 

 more or less irregularity branching radiating lines of elevation. The 

 dental lamella are short and diverge at angles of about 105 degrees. 



The interior of the brachial valve presents crural ridges, about 6 mm. 

 long, diverging at an angle of about 140 degrees, and a low, broad, 

 median elevation of about the same length. No definite muscular 

 area can be detected. 



This species is an excellent illustration of the great variation 

 in outline, length, and general convexity which can occur in a 

 single species. Fortunately, in the present case, numerous 



