HELL CREEK BEDS, CERATOPS BEDS AND EQUIVALENTS 227 



species preceded by a cross (x) are common lo these beds and the Colorado 

 Laramie] 



'^Unio ccsopijormis Whitf. 



*Unio corhiculoidcs Whitif. 



*Unio pyramidcllus Whitf. 



*Unio verrucosiformis Whitf. 



*Unio retusoidcs Whitf. 



^Unio hrownil Wliitf. 



^Unio pcrcorrugala Whitf. 



*Unio posthiplicata Whitf. 



"^Unio aldrichi White. 

 *'\Unio dancB M. and H. 

 ^\Unio holmsiana White. 



^'Unio vetusta Meek. 

 *'\Unio cryptorhynchiis White. 



^Unio hiasopoides Whitf. 



^Unio cylindricoides Whitf. 



^Unio letsoni Whitf. 



^Unio gibbosoides Whitf. 



*Unio pyramidatoides Whitf. 



*Unio siibtrigonalis Whitf. 



■\Unio hrachyopisthus White. 



^Unio cou si White. 



\Unio proavitus White. 



\Unio endliclii White. 



[About 8 undescribed species, Stanton.] 

 -\xAnodonta parallela White. 



ifAnodonta propatoris White? 

 *fSphcBrium planum M. & H. 



^Sphc^rium sp. 



fVivipams trochiformis M.. & H. 

 *xVivipan(s plicapressus White. 

 'fxT-ulotoma tliompsoni White. 

 '^fCampcloma producta White. 



'^'Campeloma vetula M. & H. 

 '^•fCampcloma idtilineata M. & H. 



\Goniobasis tenuicarinata M. & H. 

 *\Thauniastus limneiforniis White. 



\Physa copei canadensis Whiteaves. 



\ Helix vetusta M. & H, 



^Linmcea sp. 

 '^xCorbicula subelliptica M. & H. 



*Cassiopella turricida. 



*Bidinus rhomboideus M. & H. 



This table presents some interesting features. In the first place 

 it is to be noted both the "Hell Creek" and the "Ceratops beds" 

 aflford 28 forms each, of which 7 are common to the two areas, mak- 

 Proc. Wash. Acad. Sci,. August, 1909. 



