LAMELLIBRANGHIATA. 567 



Whitella sterliagensls.] 



In drawing up the above description I have made use of the original type of the 

 species which was borrowed from the museum of the Cincinnati Society of Natural 

 History. This specimen is a mold of the exterior and has been compressed in such 

 a manner that the outline is now unnaturally quadrangular, the umbonal ridge too 

 prominent and the beaks too narrow. I have compared it very carefully with the 

 northwestern specimens, which are casts of the interior, and while I admit freely the 

 the possibility of error, my conclusion for the present is that they are specifically 

 identical. 



Compared with other species of Whitella it, will be found that the shell is more 

 erect and shorter, and' the cardinal area wider than in any other known. An asso- 

 ciated form, Cyrtodonta grandis, var luculenta Sardeson, has much smaller beaks, while 

 they are also nearly in contact, the ligamental area being very much narrower. 



Formation and locality. — Upper beds of the Cincinnati group at Clarksville, Waynesville and otlier 

 localities in Ohio. The northwestern specimens were obtained from an equivalent horizon at Savannah, 

 Illinois, and Spring Valley, Minnesota. 



Whitella sterlingensis Meek and Worthen. 



PLATE XLI, FIGS. 27 and 28. 



Dolabra sterlingensis Meek and Wouthbn, 1866. Proc. Acad. Nat. Sci. Philad., p. 260; also 1868, 



Geol. Sur. 111., vol. ili, p. 339. 

 Not Cyprieardites sterlingensis ?Meek, 1873. Pal. Ohio, vol. i, p. 133. 



Original description: "Shell rhombic-cordate, being cordate in outline, as seen in 

 an anterior and posterior view, and obliquely rhomboidal, as seen from either side. 

 Posterior margin obliquely truncated, with a long slope, which is slightly convex 

 above and faintly sinuous near the middle; posterior basal extremity produced 

 obliquely backwards and downwards, with a more narrowly rounded or subangular 

 outline; basal margin ascending forward, with a moderately convex curve, and 

 rounding up more or less gradually into the very short or almost obsolete anterior 

 side; hinge line short; cardinal area moderately developed. Beaks prominent, 

 placed nearly over the anterior margin, strongly incurved and compressed antero- 

 posteriorly. Umbonal ridges very prominent, subangular, and extending from the 

 beaks obliquely to the posterior basal extremity at an angle of about 45° below the 

 horizon of the hinge, thus dividing each valve into two subequal areas, of which the 

 one behind is flattened or slightly concave between the ridge and the moderately 

 prominent postero-dorsal edge, and that in front and below it convex. (Hinge and 

 interior unknown.) 



"Greatest length, measuring obliquely from the beaks to the posterior basal 

 extremity, 2.20 inches; diameter, at right angles to the same, 1.50 inches; convexity 

 of the two valves when closed, 1.50 inches." 



