white.] LARAMIE FOSSILS OF BITTER CREEK VALLEY. 217 



23. Tulotoma tliompsoni White. 



24. Campcloma vetula Meek & Hay den. 



2o. C a myeloma multilineata Meek & Hay den? 



NOTES ON THE LARAMIE FOSSILS OF BITTER CREEK VALLEY. 



As the fossils of the different localities in Bitter Creek Valley are so 

 closely related they will all be discussed in zoological order in the follow- 

 ing notes instead of treating those of each locality separately. 



1. Membranipora? 



Upon many of the shells of Ostrea glabra Meek & Hayden (=0. icyo- 

 mingensis Meek), which were obtained at Point of Rocks, there are small 

 patches of an incrusting Polyzoan. None of them are quite perfectly 

 preserved, but they are evidently the calcareous cell-bases of a species 

 of Membranvpora or of a closely allied genus. I have detected similar 

 objects at no other locality of Laramie fossils except in the valley of 

 Bear River, but there seems to be no good reason why they may not 

 have existed with any of the many brackish- water species of that period. 

 They are interesting as indicating the continuance of a considerable 

 degree of salrness of the waters until near or quite the close of the Lara- 

 mie period. 



2. Anomia micronema Meek. 



This species has already been discussed upon previous pages as to its 

 geographical distribution and vertical range in the Laramie Group. A 

 few small examines of it were found at the Black Buttes locality, and 

 it was also found quite abundantly at the Rock Springs locality, but 

 nowhere else in Bitter Creek Valley. At both those localities it was 

 found in a separate layer associated only with Ostrea glabra. At the 

 Rock Springs locality the examples are of good size, and many of them 

 have a greater than the average convexity of form. 



At none of the numerous localities where this species has been found, 

 from the one reported by Dr. Hayden, two hundred miles east of Denver, 

 to those of Bitter Creek Valley, none but upper valves have been discov- 

 ered. It is very difficult to even suggest an explanation of this remarka- 

 ble fact, which has before been referred to. 



3. Anomia grypliorhynehus Meek. 



The locality two miles below Point of Rocks is the only one that has 

 furnished many examples of this species, although it has been clearly 

 recognized at the Crow Creek locality east of the Rocky Mountains, and 

 also at the Black Buttes and Yampa Valley localities. This shows a 

 wide geographical distribution and a considerable vertical range of the 

 species. As in the case of A. micronema, none but ujjper valves of this 

 species have been found. 



4. Ostrea glabra Meek & Hayden. 



This species has already been discussed at length on former pages, and 

 reasons given for referring these western forms to 0. glabra Meek & Hay- 

 den rather than to regard them as a separate species under the name of 

 0. wyomingensis Meek, the types of which were found at Point of Rocks. 

 If it were not for the lately obtained proof that the Judith River, Fort 

 Union, Colorado Lignite and Bitter Creek series all belong to one and 

 the same period, and the discovery of intermediate forms connecting 

 these two formerly recognized species of Ostrea, it is not probable that I 

 should have ever suspected them to be distinct. The lack of intermediate 



