UEPORT ON PAL^ONTOLOGICAL COLLECTIONS. 359 



This is one of the forms that have been very generally referred to /. proMrm«tirw< 

 from western localities, though it mav p. >ssil >1\ he distinct from that species. The 

 specimens brought in by Captain Simpson's survey are not in a very satisfactory con- 

 dition, as may be seen by the figure. Since that time I have visited the locality, and 

 collected many others. They show it to vary considerablv in form, some having the 

 hinge-line ranging much less obliquely to the axis of the umhones than others. These 

 latter show a slight tendency to have the posterior dorsal margins compressed and 

 subulate, and appear nearly equi valve, while there seem to be various gradations of 

 form between these extremes. The specimen represented bv our figure 1 a, of plate 

 IV, has the beak and dorsal margin broken away, so that the* restoration in dim shade 

 in the figure may not represent exactly the direction of the hinge-line with relation to 

 the umbonal axis. There are also among the specimens that I have seen since first 

 writing this repent, considerable variations in the ornamentation, some having very reg- 

 ular, and others irregular undulations. Some, however, such as that represented bv our 

 figures 1 fc, c, I think most probably belong to a distinct species from the majority of 

 the others, and seem to be generallv smaller and much more regularlv undulated 

 Some of these closely resemble a form that Dr. White has named /. fthuit'lhis, in Lieu- 

 tenant Wheelers report (not yet published at the time of the revision of this report, 

 ♦ November, 1875). 



If the forms like our figure la, PI. IV, are distinct from 1. problnmiticm, 1 think 

 Dr. Schiel's name, /. psciitlo-mijtihihlrs, will have to he retained for the species. These 

 shells generally have the beak more pointed and curved downward than in Kuropean 

 specimens of I. prdblenmticns, and sometimes have the hinge-line ranging at a greater 

 angle with the umbonal axis than in any figures of European specimens of that species 

 that I have yet seen. 



The figures 2 a, h, of Plate IV, represent smaller specimens, with much less 

 oblique beaks and a general outline more rounded. They are probably only the um- 

 bonal positions of larger specimens, the specific relations. of which remain doubtful. 



Locality 'and position— Bear River, near the mouth of Sulphur Creek, Wyoming. 

 Cretaceous. 



Genus ANOMIA, Linn. 



ANOMIA CONCENTEICA, Meek. 

 Plate 4, fig. 3. 

 Anomia eonernMca, Meek (July, I860), Proceed. Acad. Nat. Sci., Philad., XII, 311. 



Shell small, thin, subcircular or transversely a little oval: lateral extremities nearly 

 equally rounded ; cardinal margin rather straight, or but slightly arched ; beak very 

 small, marginal, compressed, not projecting beyond the cardinal border ; surface of 

 upper valve ornamented by moderately distinct, regular, concentric undulations, and 

 much smaller obscure lines of growth. 



Transverse diameter 0.64 inch ; length from hinge to the opposite margin, 0.50 

 inch. 



Locality and position. — Same as last. 



