CORRELATION OF THE CERATOPS BEDS. 



135 



horizon to the Fort Union. This plant-bearing horizon is perhaps 300 

 or 400 feet above the Unio bed on the divide between Lance and Light- 

 ning creeks, and probably 100 to 200 feet above the highest beds from 

 which Hatcher obtained Ceratops remains, as indicated on his map.* 

 There is no apparent break in the stratigraphy, however, nor any, decided 

 change in the lithologic character of the beds other than an increase in 

 the number of coal seams and in the proportion of clays, and the only 

 reason for separating these overlying beds is the apparent absence of 

 Ceratopsida? from them and the change in the flora. 



CORRELATION AS INDICATED BY THE INVERTEBRATE FAUNA. 



The four species of brackish- water mollusks that were collected near 

 the base of the series all occur elsewhere in the Laramie and are gener- 

 ally recognized as typical Laramie species, though very similar if not 

 identical forms are found also in older Cretaceous beds. The fresh-water 

 invertebrate fauna, occurring higher in the series, includes about 28 spe- 

 cies, of which 18 are more or less confidently identified with described 

 species, and the others are mostly new species of Unio. 



Combining the lists of our local collections and adding a few species 

 from Mr Hatcher's collections not obtained by us, the forms recognized 

 are as follows : 



f Unio dante, M. and H. 



t Umo brachyopisthus, White. 



-fCnio Goiiesi, White. 



-fUnio holmesianus, White. 



fUnio proavitus, White. 



fOhio endlichi, White. 



f Unio cryptorhynchuSj White. 



Unio (about eight undescribed species). 



Anodonta parallela, White. 



Anodonta propatoris, White (?) 



Sphaerium planum, M. and H. 



Sphxrium sp. 



Viviparus trochiformis, M.and H. 

 flulotoma thompsoni, White. 



Campeloma produda, White. 

 f Campeloma multUineata, M. and H. 



Goniobasis tenuicarinata, M. and H. 



Thaumastns limnxiformis, M. and H. 



Physa copei, var. canadensis, Whiteaves. 



Helix vetusta, M. and H. 



Limnsea sp. 



Of the 18 identified species in the above list, just half occur at Black 

 Buttes, Wyoming, in or very near the bed that has yielded the saurian, 

 Agathaumas syhestris, Cope. The large proportion of identical forms and 

 the general resemblance of the entire faunas, especially in the large num- 

 ber and great differentiation of species of Unio, makes it reasonably cer- 

 tain that the Converse county and Black Buttes beds are on nearly the 

 same horizon. The evidence of the vertebrate fossils seems to tend in the 



* American Naturalist, vol. xxx. February, 1896, pi. 111. 

 t Species marked f occur at Black Buttes, 



XX— Bull. Geol. Soc. Am., Vol. 8, 1896 



