538 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



though the exact number is difficult to ascertain, as that feature is almost 

 obsolete. 



If this is not Bhynchonella ringens of Swallow it must be a new form, 

 for there is no other representative of the genus with which it could be 

 confused. C. subtrigona Meek and Worthen, the nearest form, is yet con- 

 siderably different. However, if this reference is correct, Swallow's spec- 

 imen may have been abnormal in having so many plications on the fold, 

 as it is certainly a larger and more mature individual. 



In any case the stratigraphic value of this species remains unaltered, 

 for I can vouch for the identity of the Yellowstone National Park material 

 with a form from the lower Burlington chert of Louisiana, Missouri, which 

 passes among local collectors as R. ringens. 



R. ringens was described from the chert beds of the Encrinital limestone 

 of Callaway County. Swallow (loc. cit.) cites the species from the Burling- 

 ton of Callaway and Marion counties, while two forms, illustrated by 

 PL XLI, figs. 8«, 8b, and 11 (Geol. Surv. Missoiiri, Vol. V, Pt. II), prob- 

 ably referable to C. ringens, were found, the one in the Burlington limestone, 

 the other in the Kinderhook shales. 



Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin 

 Range, top of bed 25; J. P. Iddings and G. M. Wright. Same, bed 28; 

 J. P. Iddings and W. H. Weed. Keokuk age, Callaway County, Missouri. 

 Burlington age, Callaway and Marion counties, Missouri. Kinderhook 

 shales, Missoixri. 



CAMAROTCECHIA Hall, 1893. 



The following species occur in the lower divisions of the Madison 

 limestone. They have been referred to Hall and Clarke's genus, Camaro- 

 tcechia, although the generic characters have not been ascertained in 

 detail. Yet a process of exclusion makes it very probable that this refer- 

 ence is correct. 



All the shells have a strong median septum in the dorsal valve, while 

 the ventral valve is aseptate, but with two converging dental laminae in the 

 beak. These characters, together with their geologic position, form, nature 

 of fold and sinus, plications, etc., throw out most of the other genera and 

 subgenera into which the Rhynchonelloid type has been divided. 



