144 PALEONTOLOGY. 



plate to forms much broader posteriorly, and less oblique. They all 

 agree, however, in having the beaks much more attenuated and curved for- 

 ward than in any figures of Schlotheim's I. proUematicus I have seen. Some 

 of the broader forms agree more nearly with some of those cited above, and 

 figured by lioemer and others from western localities; but still they have 

 more pointed and oblique beaks. I suspect that this shell belongs to a dis- 

 tinct species from I. prohlematicus ; but, if so, it will probably have to be 

 designated by Dr. Schiel's name /. pseudo-mytiloides. 



Locality and position. — ^The figured specimens were brought by Colonel 

 Simpson's party from a bed of yellow Cretaceous Sandstone over a bed of 

 coal, at the mouth of SuljDhur Creek on Bear River, Wyoming. (See bed 

 number 12 of sec, on page 451, Dr. Hayden's Sixth Ann. Rep., 1873.) 



Ingcekamus (sp. undt.). 



Plate 13, figs. 4, 4 a. 



Compare I. dimidius, White (1876), Palseont. Wheeler's Surv., 179, j)!. XVI, figs. 2 a-d. 



This is a neat, symmetrical, little shell, of obliquely-ovate or mytiloid 

 form, with rather pointed, oblique, terminal beaks, and very regular, dis- 

 tinct, concentric surface-undulations. It may be a young of the last, or an 

 entirely distinct species. In some respects, it resembles one of the forms 

 figured by Mr. Conrad in the United States and Mexican Boundary Report 

 (I, plate 6, fig. 6 h) ; but it has much more regular surface-undulations, and 

 apparently more produced beaks. I was long inclined to believe it the 

 3^oungof the last described form; but it may be distinct. 



[Long since the above was written, Dr. White described from Lieu- 

 tenant Wheeler's collections, a form under the name /. dimidius, from near 

 Pueblo, Colorado, that agrees very nearly with this, and I am rather inclined 

 to believe it to be the same. He had so many specimens all of the same 

 small size, as to lead to the conclusion that it is most probably distinct from 

 /. prohlematicus. li 



Locality and position. — Cretaceous sandstone, on Sulphur Creek, near 

 Bear River, Wyoming. (Benton or Niobrara group of Upp. Mo. Sec.) 



