43(l OARBONIKKROUS KOKMATIONS AND FAUNAS OF COLORADO. 



:uiil it frequently happens that the outer layer adheres to the matrix unci the inner 

 to {he int(M'nal <iast of specimens. The direction of tiui <^-rowtli linos indicates that 

 the posterior outline is that of Aviculojmma, having- a i)ackward swin^ and an 

 obtuse posterior cardinal angle. This feature is liable to variation, the posterior out- 

 line in some specimens being more nearly a right angle. The one phase is repre- 

 sented by lig. 1 of PI. IX, and the other by tig. 2. In restoring tiic outline, which 

 has been done in the case of these two figures, it is difficult to estinmtc from the 

 existing parts what shape the missing ones would have had; and consequently I sus- 

 pect that the backward sweep in tig. 1 is represented as somewhat too great. The 

 shell in fig. 2 is largelj^ exfoliated, but one small fragment shows the surface to have 

 been marked with spaced lamellas like that represented by fig. 1. 



This shell resembles quite closelj' the figures given by Beede of the species from 

 the Nebi'aska Permian, which he describes as Aviculo2nnna nehraskensw. Certain 

 differences in detail of shape are obvious, but they hardly, it seems to me, validate 

 the recognition of my Colorado specimens as belonging to a distinct species. 



Locality and horizon. — San Juan region (stations 2341,2342); Rico formation. 



CH^NOMYA Meek, 1864. 

 CHiENOMTA LEATENWOETHENSis Mccli and Haydcn. 



1858. AUorismaf leavenworthensis. Meek and Hayden, Acad. Nat. Sci. Philadelphia, Proc, p. 263. 



Coal Measures: Leavenworth, Ivans. 

 1864. Chxnomya leavenworthensis. Meek and Hayden, Smithsonian Cent. Knowledge, vol. 14, No. 172, 

 p. 43, pi. 2, figs. la-c. 



Coal Measures: Leavenworth, Kans. 

 1866. Allorisma leavenivorthensis. Geinitz, Carb. und Dyas in Nebraska, p. 15. 

 1872. Chxnomya leavenworthensis. Meek, U. S. Geol. Surv. Nebraska, p. 216, pi. 2, fig. 9. 



Upper Coal Measures: Rock Bluff, Nebr. ; Leavenworth, Kans. 



Coal Measures: Iowa, Missouri, Illinois. 

 1895. Chxnomya leavenworthensis. Keyes, Missouri Geol. Surv., vol. 5, p. 131. (Date of imprint, 1894.) 



Upper Coal Measures: Kansas City, Mo. 

 1900. Chxnomyd leavenworthensis. Beede, Univ. Geol. Surv. Kansas, Kept., vol. 6, p. 172, pi. 19, figs. 

 3-.3b. 



Upper Coal Measures: Kansas City, Lawrence, Kans. 



Two specimens from station 2200 (Big Percent Creek, in the San Juan region) 

 by their general configuration and widely gaping posterior extremities leave little 

 doubt of their generic relationship. They are, however, considerably crushed, and 

 there is an element of specific uncertainty in tlieir identification. Similarl}- tinc- 

 tured with doubt is the identification of a single small specimen from station 2219 

 (south of Marguerite Draw). Another isolated specimen from Sinbads Valle}' (sta- 

 tion 2285), imperfect, though rather well preserved, probably belongs to the same 

 species as the above. 



