DESCRIPTIONS OF SPECIES. 383 



surface of Sp. centronatus the fine concentric striae dominate the radiating ones, but 

 in Sp. ioonenms the radiating- striae seem to be dominant. However, these differ- 

 ences are by no means marked, and although exhibited by the few more perfect 

 examples which have come before me, it is doubtful if they would be maintained in 

 even the limited measure in which they there obtain, in a more extended series. 



Our collections show that this species is found at a number of localities, and the 

 evidence seems to indicate that it is seldom associated with Sp. rockyinontanus. My 

 material is not satisfactorj'^, as often but a single individual is known from a locality, 

 and the preservation poor. Yet I believe that in most cases the determinations 

 made would be substantiated if more abundant and better preserved specimens could 

 be obtained. This species is especially abundant in the San Juan region, and its 

 most typical representatives are found at the base of the Hermosa formation and in 

 the Molas formation. Two examples from the base of the Hermosa are figured on 

 PI. VI. 



Locality and horizon.— ^&\\ Juan region (stations 2187, 2197, 2201, 2202?, 2206, 

 2209, 2213, 2214, 2219, 2243, 2246, 2247, 2284?, 2331?, 2332, 2334); Molas formation, 

 lower, middle and upper portions of the Hermosa formation. Ouray (station 2194); 

 Hermosa formation. Crested Butte district (station 2246). Grand River region, 

 North Fork of Eagle River (station 2289); base of the Maroon formation. 



Spirifer rogkymontanus Marcou. 



PI. XVI, figs. 4, 4a, 5, 5a, 6, 6a, 7, 7c. 

 18.58. (March.) Spirifer rochjmontani (pars). Marcou, Geol. North America, p. .50, pi. 7, figs. 4c-4e, 

 (non 4-4b?). 

 Mountain limestone: Tigeras, N. Mex. 

 1858. (December.) Spirifer opimus. Hall, Geol. Surv. Iowa, vol. 1, pt. 2, p. 711, pi. 28, figs, la, b. 

 Coal Measures: Ohio, Maryland, Iowa, etc. 



1860. Spirifer subveniricosd . McChesney, Desc. New Spec. Pal. Foss., p. 44. 

 Coal Measures: Big Creek, Indiana, near New Harmony. 



1861. Spirifer rockymontani. Newberry, Ives's Colorado River Expl. Exped., p. 127. 

 Upper Carboniferous limestone: New Mexico. 



1865. Spirifer s-ubventricosa. McChesney, Illustrations New Spec. Foss., pi. 1, figs. 4a, b. 

 1868. Spirifera opimus. McChesney, Chicago Acad. Sci., Trans., vol. 1, p. 35, pi. 1, figs. 4a, b. 

 Coal Measures: Big Creek, near New Harmony, Ind. 



1874. Spirifera opima. Derby, Cornell Univ., (Science) Bull., vol. 1, No. 2, p. 15, pi. 1, fig. 4; pi. 2, 



fig. 7; pi. 4, fig. 12. 

 Coal Measures: Bomjardim, Paredao, and Itaituba, Brazil. 



1875. Spirifer {Trigonolreta) opimus? Meek, Pal. Ohio, vol. 2, p. 329, pi. 19, figs. 14a, b, c, d, (e?). 

 Coal Measures: Ohio, Illinois, Iowa, Missouri, West Virginia, and Eocky Mountains. 



1875. Spirifer rockymonlanus. White, U. S. Geog. Geol. Surv. W. 100th Mer., Rept., vol. 4, p. 1.34, 

 pi. 11, figs. 9a-d. (Whole volume published in 1877. ) 

 Carboniferous: North Fork of Lewiston Canyon, Oquirrh Range, and on west face of Oquirrh 

 Range, Utah; near Santa Fe, N. Mex. 



