218 KEPOET UNITED STATES GEOLOGICAL SURVEY. 



forms west of tlie mountains like those "which "were found hi Eastern 

 Colorado is suggestive that there may after all be really two species, 

 especially so since only thin, small examples are found at the locality 

 two miles west of Point of Rocks. In Professor Powell's Report on the 

 Geology of the Uinta Mountains I gave the name of 0. insecuris to these 

 last-mentioned examples, but comparison of my types directly with those 

 of 0. glabra shows too little difference to be satisfactorily regarded as 

 specific. Comparison of large collections made at the typical localities, 

 Point of Rocks and Black Buttes Station, with the types themselves, 

 leaves no doubt in my mind that 0. wyomingensis Meek and 0. arcuatilis 

 Meek are specifically identical. It will of course be understood that I 

 regard such forms as the types of 0. glabra Meek & Hayden, 0. subtri- 

 gonalis Evans & Shumard, and 0. insecuris White as young examples of 

 the species, and 0. wyomingensis Meek as adult forms of the same. By 

 these and other remarks on previous pages it will be seen that at preseut 

 I recognize only one species of Ostrea in all the Laramie Group, unless 

 the obscure one that is found in Bear River Valley, yet to be noticed, 

 shall prove to be distinct from 0. glabra. 



5. Volsella (BracJiydontes) regularis White. 



A few large but imperfect examples of this species were found just 

 east of Rock Springs, which is the only locality in Bitter Creek Yalley, 

 at which it was .discovered. See further remarks under the head of notes 

 on the Laramie fossils of Crow Creek Valley. 



6. JJnio couesi White. 



This is one of nine or ten species of JJnio that have been found asso- 

 ciated in one and the same layer at Black Buttes Station, and also asso- 

 ciated with Corbicula (Leptesthes) fracta, Weritina volvilineata, Neritina 

 ( Velatella) baptista and Melania wyomingensis. None of these species of 

 JJnio have been discovered at any other locality west of the Rocky Mount- 

 ains, but two of them, JJ. cryptorliynclms White and JJ. danw Meek & 

 Hayden, have been somewhat satisfactorily identified with the typical 

 forms from the Upper Missouri River region. This is the largest species 

 of the genus that has yet been found fossil in any strata of the West. It 

 was originally described by me under the name of JJ. petrinus in Powell's 

 Report on the Geology of the Uinta Mountains, p. 125, together with 

 Nos. 7 and 8 following. That name being preoccupied, it was changed 

 to JJ. couesi, in Bull U. S. Geol. and Geog. Sur. Terr., vol. hi, p. 605. 



7. Unio proplieticus White ) g k mider ^ 6# 



8. JJnio braclnopistlms White. ) 



9. JJnio proavitus White. 



This species, together with Nos. 10 and 11 following, are described in 

 Bull. U. S. Geol. Sur. Terr. vol. hi, pp. 603 and 604. 



10. JJnio liolmesianus White. 



11. Unio endliclii White. $ See remarks mder ^°' 6 " 



12. JJnio aldrichi White. 



This species, together with No. 13 following, are described in Bull. U. 

 S. Geol. Sur. Ter. vol. iv, pp. 709 and 710. 



13. JJnio goniambonatus White. 

 See remarks under No. 6. 



14. JJnio cryptorliynclms White. 



Some imperfect examples found associated with the foregoing species 

 appear to be specifically identical with the types of JJ. cryptorliynclms 



