246 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Mr. Meek describes it and figures an imperfect example in the United 

 States Geological Survey 10th Parallel. 



32. Spirorbis? 



Near Mellis Station some examples of a minute coiled shell resem- 

 bling a Spirorbis were found attached to ZPiiio vctu.stu.s and oilier associ- 

 ated shells. It is possible that they are the first coils or young - examples 

 of the Planorbis, No. 15, but they seem to have been of a parasite or 

 commensal habit. Water that was salt enough for Corbula, Membrani- 

 pora, &c.j would no doubt have been congenial for Spirorbis. 



33. Cypris ? 



Multitudes of casts of a species of Cypris were found in the gray 

 clayey shale, 40 feet above the principal bed of coal at the Evanston coal 

 mines, belonging to the upper Laramie beds. 



In this soft, clayey shale were also found, besides the Splicerium and 

 Cypris already mentioned the casts of numerous other small shells, mostly 

 those of Physa or Bulinus ; and in addition to these, a few cycloid fish- 

 scales ; also associated with ISTos. 37 and 38 numerous minutes nutlets of 

 a species of Chara were found. 



Besides the species enumerated or referred to in the foregoing list, 

 there are among the collections, especially those from the upper beds, 

 fragments that indicate the existence of several yet undetermined species 

 of invertebrate fossils. 



In all the other collections of Laramie fossils that have been discussed 

 in this report some species are represented which connect the strata of 

 the different localities from which they respectively came, as unmistaka- 

 bly belonging to the great Laramie Group ; but a comparison of the col- 

 lections from the lower beds of Bear Eiver Valley with all the other 

 collections of Laramie fossils is one entirely of contrast, so far as specific 

 identity is concerned, unless the Bulinus mentioned under ~So. 17 be an 

 exception. Moreover, as has already been mentioned, these lower beds 

 of the Bear Eiver Laramie contain two or three molluscan types of generic 

 or subgeneric value, that have never been found elsewhere, besides some 

 other modifications of type perhaps of less value than the others, but 

 still sufficiently characteristic. 



Inquiring into the inhabitancy of the whole fauna of these lower beds 

 we do not find an indication that its condition, so far as saltness of the 

 water is concerned, was materially different from that of the brackish- 

 water fauna of the Laramie Group in general, there being always, and in 

 the case of both faunse, a mixture of both brackish and fresh water forms, 

 with some palustral pulmonates and an occasional land shell. The 

 marked difference, then, between the invertebrate fauna of the lower beds 

 of Bear Eiver Laramie and that of the group in general is not such as is 

 produced by a change in the saltness or by a complete freshening of the 

 inhabited waters ; but it is evidently due to other causes. My own inves- 

 tigations of these strata have been far too limited to warrant any present 

 discussion of the causes that have produced these faunal differences, but 

 there seems to be little room for doubt that it was due in large part to 

 conditions consequent upon the proximity and character of the western 

 shore of the Laramie sea. It will also be remembered that the Cretaceous 

 fauna of the Coalville series, which occupies a similar relative geological 

 position, shows almost if not equally as great a contrast with that of its 

 assumed equivalent strata which occupy the same regions farther east- 

 ward with the various Laramie strata herein discussed. But after all the 

 inquiry naturally arises, are these Bear Eiver beds properly referable to. 

 the Laramie Group, and, if so, are they true equivalents of those Lara- 



