400 GEOLOGY OF THE BLACK HILLS. 



that species, although from the figures and description given in the Synop- 

 sis of the Organic Remains we certainly should not have done so. We had 

 previously tried to see Dr. Morton's types in the collections at Philadelphia, 

 but did not succeed, owing to the absence of persons having charge ; con- 

 sequently we were compelled to depend upon the figures and descriptions 

 above referred to until we received a copy of Mr. Meek's excellent work, in 

 which he describes these forms and figures, the types above referred to. 

 But we are not prepared to identify them with I. cripsii Mantell, nor with 

 any shell conforming to Mantell's description ; and the forms referred by 

 authors to that species are so variable, that we can rely only upon the orig- 

 inal type specimens. 



Formation and locality. — In limestone of the Fort Pierre Group, Chey- 

 enne River, near Box Elder Creek, and on Beaver Creek, two to three miles 

 west of the Black Hills. 



INOCEBAMUS TENUILINEATUS. 



Plate 9, figs. 12, 13. 



Inoceramus tenuilineatus H. & M., Mem. Acad. Arts and Sci., vol. viii, p. 387, Bl. 2, fig. 3. 

 Inoceramus tenuilineatus (H. & M.) Meek, Bal. IT. S. Geol. Surv. Terr., p. 57, Bl. 12, fig. C. 



Shell of rather large size, transverse, subovate or rhomboid-ovate in 

 outline, with very ventricose, almost inflated valves, and large, inflated, 

 slightly prominent, incurved, and nearly terminal beaks ; hinge line shorter 

 than the length of the shell below and rounded at the posterior extremity ; 

 cardinal and basal margins subparallel ; the latter gently rounded in the 

 middle and a little more abruptly so toward the ends ; anterior end broad, 

 obliquely truncate in a side view, projecting a little in the lower part 

 be von d the line of the beaks, forming- with the cardinal line an angle of 

 from 95° to 120° in different individuals, but generally not more than 100°; 

 posterior margin rounded, most strongly from below ; anterior slope of the 

 valves very abrupt and on some specimens nearly vertical for one-half the 

 depth of the valves ; posterior slope more gradually declining from the 

 prominent umbonal portion of the valve, giving a somewhat cuneate form 

 to the posterior half of the shell when viewed in a cardinal profile. 



Surface of the shell marked by, sometimes indistinct, but often very 



