294 GEOLOGICAL SURVEY OF THE TERRITORIES. 



If it should be thought desirable to make it the type of a distinct sub- 

 genus, it may be called Gorbicula ( VeloritinaJ Durlceei. In the same 

 way, if the proposed sections, of Unto should be sustained, the curiously 

 plicated species, described by me under the name U. belliplicata, may be 

 called U. (LoxopleurusJ belliplicatusA 



I have elsewhere proposed, in manuscript, to make my Melampu&pris- 

 cus from this formation, the type of a new group, under the name Bliy- 

 toplwrus prisms, on account of its peculiar costated surface, smooth 

 outer lip, and single well-developed plait, and another obscure one, on 

 the columella. 



Of the species of Tiara, already mentioned from this rock, thousands 

 of specimens have been obtained, and yet it is remarkable that not a 

 single one of them shows the lip about the lower part of the aperture 

 unbroken, and entirely free from the matrix. Some of those I have re- 

 cently seen, however, appear to show a kind of angularity about the 

 base of the aperture not seen in the typical forms of Tiara, and some 

 appearance of a peculiar furrow along the outer edge of the base of the 

 columella. If these are not due to accident — and they certainly seem 

 not to be — it may be found that this shell should be regarded as the 

 type of a sub-genus, bearing somewhat similar relations to Tiara to 

 those existing between Gonidbasis and the elongated old world Melanians. 

 If so, it may be called Tiara (Pyrgulifera) lmmerosa.% 



Of course, comparisons of the shells from this formation with those 

 of the tertiary beds of the Atlantic and Pacific slopes, afford no aid 

 whatever in fixing its precise position in the series, because the species 

 from the latter are, almost without exception, marine types. There is 

 less difficulty, however, in drawing parallels between it and the tertiary 

 deposits of the Upper Missouri country, by a comparison of fossils, al- 

 though the species are mainly different, so far as yet known, in these 

 two districts. At least two of the known forms, however, from the Utah 

 and Wyoming beds under consideration, are believed to be specifically 

 identical with species found in the oldest beds referred to the tertiary 

 at the mouth of Judith Eiver on the Upper Missouri, under the name 

 Fort Union Group. These are Unio priscus and Viviparus Gonradi. In 

 addition to this, the fossils at these two localities are in precisely the 

 same state of preservation, and have a more ancient appearance than 

 those of the later deposits of both districts, while they also agree exactly 

 in their mixture of brackish and fresh- water characters. Again, at both 

 localities, these deposits are intimately associated, as already stated, 

 with what appears to be the latest of the cretaceous series ; while in 



I I have had no opportunity to consult Spix's work in which he proposed the group 

 Diplodon, but had supposed from the strongly alate-shell figured by Sowerley as an 

 illustration of the same, that it was founded on a widely distinct type from our Utah 

 shell. From the diagnosis of Diplodon, given by H. and A. Adams, however, I am led 

 to think it may possibly include our type, though I cannot believe the North American 

 species ranged by the above-named authors should be placed in the same section with 

 our species. 



X Since these remarks were in type and issued in pamphlet form, Mr. Conrad kindly 

 sent me a sketch of a specimen of this species at the Philadelphia Academy of Science, 

 showing more of the lip and base of the aperture than I had seen, and expressed the 

 opinion that it is a good genus. Soon after I succeeded in working the matrix from 

 the aperture of a perfect very large specimen, and from this and Mr. Conrad's sketch, 

 the inner lip is seen to be quite thick all the way up, but particularly below, and the 

 narrow base of the aperture sinnous. My specimen also shows that there is a shallow 

 marginal sinus of the outer lip at the termination of the shoulder, while below this it 

 is prominent. It is therefore evident, that with the distinctly turreted spire, shouldered 

 and coronate wheels, as well as the general aspect of Tiara, in its thickened inner 

 lip and some other characters, it resembles Litkasia, and constitutes a distinct genus 

 from both, in which opinion Mr. Conrad and Professor Gill concur. 



