INVERTEBRATE TALyEONTOLOGY. 63 



Inoceramus problematicns, var. avicnloides, M. & H. 



Plato 0. fiR.4. 

 Inoceranms avicnloides, Meek and Hayden (May. 1860), Proceed. Acad. Nat. Sci. Philad., XII, 181. 



Shell obliquely subovate, compressed, very thin, siibequi valve, very 

 inequilateral; anterior border sloping from the beaks obliquely backward 

 and downward, with a more or less convex outline ; posterior basal margin 

 regularly rounded ; posterior dorsal slope usually convex in outline below, and 

 concave above, forming an angle of about 45° with longest diameter of the 

 shell, compressed and generally somewhat alate posteriorly ; beaks oblique, 

 rather small, nearly terminal. Surface ornamented with small, more or less 

 regular, concentric undulations, and finer strise of growth. Right valve com- 

 pressed ; beak scarcely projecting above the hinge-margin. Left valve a 

 little more convex ; beak convex, rather pointed, incurved, and slightly more 

 prominent than that of the other valve. 



Length, measuring from the beak of the right valve obliquely back to 

 the postero-basal extremity, about 3 inches ; breadth across, at right angles 

 to the length, 1.70 inches ; convexity, about 0.88 inch. 



The right valve, figured on our plate, under the above name, is the form 

 for which we at one time proposed the name I. avicnloides. Later compari- 

 sons have led to the conclusion that it should probably be included as a 

 variety of /. problematicus, Schlotheim. I should remark, however, that the 

 left valve is proportionally more convex, and its beak more prominent than is 

 usual in Schlotheim's species ; while, as may be seen by our figure, its 

 hinge is proportionally longer, and its posterior dorsal region more alate. 

 There are among the specimens, however, so many gradations between this 

 form and the typical I. problematicus, such as those represented by our figs. 3, 

 a, b, of the same plate, that it seems hardly possible to separate them specifi- 

 cally. 



Locality arid, position. — The specimen figured on pi. 9 was obtained on 

 Little Blue River, near the Kansas and Nebraska line, where it was found 

 associated with the typical I. problematicus. Both also occur near Big Blue 

 River, in Nebraska: on Republican River, Kansas, and other localities in that 

 region. So far as yet determined, they are both only found in the light- 



