LOWEE CAEBOXIFEKOUS FOSSILS. 573 



STRAPAROLLUS Montfort, 1810. 



Straparollus utahensis Hall and Whitfield. 



PI. LXVI, figs. 10a, 106, 10c. 



Uuomphalus (Straparollus) utahensis Hall and Whitfield, 1877: King's U. S. Geol. 

 Expl. 40th Par., Vol. IV, p. 259, PI. IV, figs. 20-23. 



This genus is represented in the collection from eight or ten localities, 

 but the specimens are in so poor condition, being worn or broken, that a 

 specific identification was a matter of difficulty. The beds from which 

 the material was derived are mostly the lower strata of the Madison lime- 

 stone, but some specimens, indistinguishable from the others in their present 

 imperfect condition, occur near the very top of the same formation. 



It was evident at first sight that the Yellowstone National Park form 

 was close to Euomphalus luxus White, and Eu. utahensis Hall and Whitfield. 

 After a careful comparison of the three' types the balance of the evidence 

 seemed to favor an identification with Eu. utahensis, and a section throug'h 

 one of the specimens justified the conclusion. It will be remembered that 

 the two species just mentioned are both from the Rocky Mountain region, 

 occurring in Waverly rocks, and often found at the same locality. Eu. luxus 

 is somewhat smaller than Eu. {Straparollus') ■utahensis. The whorls are 

 flattened on top, with a slight distal carination. In S. utahensis, however, 

 there is a strong carination on the summit of each whorl, from which the 

 sides slope away nearly plane, one toward the center, the other toward 

 the periphery. This proved to be the case with the specimen sectioned, 

 but it is not at all improbable that some of the other smaller specimens 

 may belong to Eu. luxus. 



The shell of S. utahensis is thin, but thickened on top and on the two 

 sides to form the carinations (PI. LXVI, fig. 10c). The outer side of each 

 whorl as well as the top is carinated, and the shell on the inner side is also 

 considerably thickened, but indented to receive the carina of the preceding 

 whorl. The interior cross section, therefore, is circular or elliplical, and 

 all distinguishing characters are lost when the shell is reduced to a cast. 



This species should be compared with Euomphalus obtusus Hall (Geol. 

 Surv. Iowa, Vol. I, Pt. II, p. 523), which was described from the Oolitic 

 limestone of Burlington, Iowa. 



