CRETACEOUS FOSSILS. 143 



ally longer and more depressed than any otherwise nearly allied species with 

 which I am acquainted. 



Locality and position. — North Platte River, above Platte Bridge, in Da- 

 kota Territory; from the Cretaceous formation No. 2 or 3 of the Upper ]\Iis- 

 souri section. Discovered by Colonel Simpson. Museum of the Smith- 

 sonian Institution. 



INOCEIIAMUS PROBLEMATICUS, Sclllot.l 



Plate i:5, figs. 2 .and 2 a. 



MytilUcH prohlematicus, Sclilotli. (1S20), Tetref., 312. 



Inoccramus myUloides, Sowerby (1823), Min. Couch., V, Gl, pi. 442; Goklf. (1S3C), 



Petref., II, 118, tab. cxiii, figl 4. 

 Catillus Schlotheimii, Neilssou (1827), Petref. Suecaua, 19. 

 Caiillus mytiloidcs, Deshayes (1830), Encyc. Metb., II, pi. 211. 

 Inoceramns problemaHcvs, cVOibigny (1843), Paleont. Fr., Ill, 510.— Meek (1873), 



Ilaydeii's Sixth Report, 470; and (187G) iu Col. Siaipsou's Report Expl. across 



Great Basin of Utah, 358, pi. 4, tig. 1 a. 

 Compare I. mytiloidcs, Roenier (1852), Kreid. von Texas, CO, pi. vii, fig. 5 (= I. myti- 



/ojjsis, Conrad (1857), U. S. and Mex. Bound. Report, 1, 152, pi. 5, figs. G«, and G h; 



also with I. pmiilo-mytUokles, Scbiel (1855), Pacitic Railroad Reports, II, pi. 3, 



fig. 8. 



Shell obliquely subovate, extremely inequilateral, rather compressed, 

 and apparently nearly equivalve; anterior margin tiiincatedor sloping very 

 obliquely backward from the beaks to near the middle, where it passes im- 

 perceptibly into the base; basal margin sloping obliquely backward and 

 rounding into the posterior basal extremity, Avliich is generally narrowly 

 rounded; hinge-line rather short and very oblique to the longer axis of the 

 valves; posterior dorsal margin sloping obliquely with a more or less convex 

 outline from the posterior extremity of the hinge to the posterior basal mar- 

 gin; beaks very oblique, acutely jxiinted, incurved, and terminal. Surface 

 oi-uiimenJed with small, more or less regular, concentric undulations and 

 stria". 



At the time I wrote the above description, I had seen only the figured 

 specimens, ^^■hich are much broken and distorted. Since that time, I have 

 ha,d an opportunity to collect and examine a large series at the same locality 

 in Wyoming from which those figured on plate 1 3 were collected. These 

 additional specimens show that this shell varies greatly in form; there being 

 apparently an unbroken series from specimens like those figured on our 



