208 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



NOTES ON THE LAEAMTE FOSSILS OF YAMPA YALLEY. 



Tlie fossils of this list occupy a distinct horizon of limited vertical ex- 

 tent and probably not more than four or live hundred feet below the 

 top of the Laramie Group. The Ostrea, however, appears to have a 

 greater vertical range than the other fossils of the list do, as I found a 

 few examples of it in different places, from one to two hundred feet be- 

 low the horizon of the other species. All the species appear to be inti- 

 mately associated together, except that the gasteropods appear to be 

 mainly or wholly confined to a single layer, but that layer has other 

 layers containing the other fossils, both above and below it. 



1. Ostrea glabra Meek & Hay den. 



Most of the specimens of this species which were obtained in Tampa 

 Valley are comparatively large, massive shells, being fully adult. They 

 are in all respects like those which have been obtained from the same hori- 

 zon at Point of Eocks, something more than 100 miles to the northwest- 

 ward, and which were described by Meek as 0. wyomingensis. It has been 

 shown on a previous page that in the Laramie strata of Eastern Colo- 

 rado intermediate forms are found associated with typical forms of 0. 

 glabra and 0. tvyomingensis that connect these two types unmistakably. 

 I therefore retain the name 0. glabra as having priority of date, although 

 it is seldom that any specimens are found in the Laramie strata west of 

 the Eocky Mountains that closely resemble the types of 0. glabra which 

 were selected for illustration by Meek and Hayden. This species is ex- 

 tremely variable, even for one of the genus Ostrea, and there is much 

 reason to believe that not only 0. glabra Meek & Hayden, O. subtrigo- 

 nalis Evans & Shumard, O. ivyomingensis Meek, as already suggested, 

 but O. arcuatilis Meek and 0. insecura White also belong to one and the 

 same species. But this subject will be further referred to in connection 

 with a discussion of the collections made in the valley of Bitter Creek. 



2. Anomia micronema Meek. 



The specimens of this species which were obtained in Tampa Valley 

 have a smaller average size than those which were obtained from the 

 Laramie strata east of the Eocky Mountains, and smaller also than those 

 found at Eock Springs in the valley of Bitter Creek, which occur there 

 at a somewhat lower horizon in the Laramie series ; but they are doubt- 

 less specifically identical at all these localities. See further remarks 

 under the head of notes on the Laramie fossils of Crow Creek on a pre- 

 vious page. 



3. Anomia gryplwrJiyncJius Meek. 



Two or three examples only of this species were found in the Tampa 

 Valley. It is a rare species at all places except the original locality in 

 Bitter Creek Valley. See further remarks under the head of notes on 

 the Laramie fossils of Crow Creek and Bitter Creek Valleys. 



4. Volsella (Brachydontes) regularis White. 



A couple of fragments only of this species were obtained in Tampa 

 Valley, where they were found mingled with the shells of Ostrea and 

 Corbicula. The type specimens were found in the valley of Crow Creek, 

 under which head the species is more fully noticed ; but it has been recog- 

 nized at several places west of the Eocky Mountains in Colorado and 

 Wyoming. 



5. Corbicula occidentals Meek & Hayden. 



This species was originally described by Meek & Hayden from the 

 Judith Eiver Group in the Upper Missouri Eiver region, and it is also 



