574 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Formation and localit}- : Madison limestone, east side of Gallatin River, 

 west of Electric Peak ; divide between Gallatin River and Panther Creek, 

 Gallatin Range ; summit of Antler Peak, Gallatin Range; amphitheater east 

 of Bannock Peak, Gallatin Range, bed 30; W. H. Weed. Crowfoot Ridge, 

 Gallatin Range, top of bed 26, lower part of bed 27, bed 28, bed 31 ; J. P. 

 Iddings and W. H. Weed. Waverly age, Dry Canyon, Oquirrh Mountains; 

 Ogden and Logan canyons, Wasatch Range, Utah. 



PLATYCERAS Conrad, 1840. 



This genus is represented by specimens which are rather scarce 

 numerically and as to size much below the average. Taken as a whole, 

 they are closely similar to the group of Waverly Platycerata figured by 

 Keyes in Geol. Surv. Missouri, Vol. V, PI. LIII, figs la-Id, 2-8, 9a, 9b. In 

 a genus where the species vary so enormously within themselves — where, 

 in fact, it may almost be said that there are no species — my material is 

 much too scanty and fragmentary to show the range of specific variation 

 and afford the concept of a specific type. Accordingly, no elaborate effort 

 has been made to identify the material with existing species, much less to 

 propose new names, and it has seemed best to describe each form without 

 using specific appellations. 



Form A. 



This form is found on Crowfoot Ridge, Gallatin Range, from the top 

 of bed 24. It is small and loosely coiled. The apex is wanting, but the 

 whole specimen appears to have completed little more than half a turn. 

 The apical portion is twisted slightly to the left (looking at the anterior 

 peripheral face), and the base expands rapidly, but unsymmetrically, flaring 

 a little more on the side toward which the apex is turned — the left. There 

 is a broad carination on the front face, delimited by the two shallow 

 grooves. Aperture subcircular. This form appears to be close to P. 

 cornuforme, 1 Winched, but that shell is said to be planorboid, while in this 

 the apex is distinctly turned to the left. It also resembles P. vomerium 1 of 

 the same author in size and in the nature of the carination. Both these 

 species are of Waverly age. 



1 Winchell, 1863: Proc. Acad. Nat. Sci. Philadelphia, pp. 18, 19; and Keyes, loc. cit., PI. LIII, 

 tigs. 3a, 36. 



