520 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



of 1 cm. Dissepiments more slender, regular, uniform, twenty to twenty- 

 three in the space of 1 cm. Fenestrules a little longer than wide, subquad- 

 rate in outline, angular. Zooecia in two rows, circular, about three to each 

 fenestrule, amounting to between fifty and sixtv in the space of 1 cm. It 

 will be seen that while the description shows this form to be close to several 

 known species (A. distans, A. invaginatus of the Chester, A. negligens of the 

 Keokuk), it is not specifically the same as any of them. Several other 

 Fenestellids occur in the same beds, but their condition does not warrant the 

 attempt to identity them. 



Formation and locality : Madison limestone, south of Forellen Peak, 

 Teton Range ; S. L. Penfield. 



CRANIA Retzius, 1781. 

 Crania l^vis Keyes. 

 PL LNVIII, fig. la. 

 Crania lewis Keyes, 1894: Geol. Surv. Missouri, Vol. Y, Pt. II, p. 40. 



The single specimen by which this species is represented is somewhat 

 crushed, but appears to be of an elliptical or subcircular shape, the larger 

 diameter being 23 mm., the shorter about 19 mm. Beak lying in the short 

 diameter, and eccentric with regard to the long one. Side nearest to it some- 

 what truncated. Convexity moderate, about 7.15 mm. Surface smooth, 

 without radiating striae, but with fine concentric lines of growth. 



Keyes's description, which is unaccompanied by fig-ures, is very brief 

 and contains little which is of value in identifying species. According to 

 the original description, C. Icevis is rather above the medium size, somewhat 

 depressed, apex subcentral, outline subcircular, truncate. Smooth but for 

 fine concentric lines. In all these points the Yellowstone National Park 

 form agrees with C. Icevis, which is furthermore said to occur in rocks of 

 Waverly and Burlington age. 



Only four species of Crania have been described from Carboniferous 

 strata : Crania Icevis Keyes, Crania rowleyi Curley, Crania permiana Shu- 

 mard, and Crania modesta White and St. John. The first two are of 

 Waverly age, the last two of Upper Carboniferous. It is extremely 

 improbable that either C. modesta or C. permiana would be found in these 

 beds associated with low Lower Carboniferous fossils, while C. rowleyi is 



