DESCRIPTIONS OF SPECIES. 427 



theless I hare accepted it provisionallj;' in identifying m}' Colorado specimen. The 

 latter has a length of .33 mm. and a width slightl}' greater. The shape is thu.j shown 

 to be a little transverse, and it is nearly bilaterallj- symmetrical. The convexity is 

 moderate and is greatest just below the beak, which is small, incurved, and but 

 slightl}' projecting. The hinge line, which is straight and about 18mm. long, merges 

 easilj' into the nearly circular outline. 



Comparing this specimen with Ke5'es's figure the straight hinge line seems to be 

 a trifle longer and the beak incurved instead of erect. Supposing it to be the oppo- 

 site valve the shape is otherwise nearly identical. 



Both of these forms differ from the type of P. pertemds in being more nearly 

 circular. My specimen difl'ers also in having the hinge line represented on both sides 

 of the beak. 



Inasmuch as the structural characters of these forms are not known, and as 

 dependence has to be placed in determining their genei'ic position upon their general 

 configuration, it seems that they would be more correctly referred to Posidoniella 

 than to Posidonomyu. 



IjOcality and horizon. — San Juan region (station 2341); Rico formation. 



PSEUDOMONOTIS Beyrich, 1862. 

 PsEUDOMONOTis HAWNi Meek and Hayden. 



1858. Monotis havmi. Meek and Hayden, Albany Inst., Trans., vol. 4, p. 76. 

 Permian: Near mouth of Smoky Hill Fork of Kansas River and Helena, Kans. 



1859. Monotis hawni. Meek and Hayden, Acad. Nat. Sci. Philadelphia, Proc, p. 28. 



Upper Coal Measures: South of Kansas Falls, Smoky Hill River, and Cottonwood Creek, Kansas. 

 1864. Eumicrotk hmmi. Meek and Hayden, Smithsonian Cont. Knowledge, vol. 14, No. 172, p. 54, 



pi. 2, figs. 5a-c.. 



Permian: Near mouth of Smoky Hill Fork of Kansas River and between there and Council 

 Grove; also on Cottonwood Creek, Kansas. 

 1884. Eumicivtis liawni. White, Geol. Surv. Indiana, 1.9th Rept.., p. 142, pi. 30, fig. 10. 



Upiser Coal Measures: Indiana. 

 1886. Eumicrotis hmmi. Heilprin, 2d Geol. Surv. Pennsylvania, Ann. Rept. for 1885, p. 455. 



Upper Coal Measures: Mill Creek limestone, Wilkesbarre, Pa. 

 1886. Eumicrotis hiiii-ni. Heilprin, Proc. and Coll. WyomingPIist. and Geol. Soc, vol. 2, pt. 2, p. 271. 



Upper Coal Measures: Mill Creek limestone, Wilkesbarre, Pa. 



1899. P.ieuclomonotiii ci. hmmi. Beede, Kansas Univ. Quart., vol. 8, No. 2, p. 83, pi. 19, figs. 1-1/. 

 Upper Coal Measures: Turner, Wyandotte County, Kans.; Clemento, Topeka, Lawrence, Kans. 



1900. Pseudomonotis havini. Beede, Univ. Geol. Surv. Kansas, Rept, vol. 6, p. 132, pi. 13, figs. 11-llc; 



pi. 15, figs. 1-lf, 2, 2a. 

 Upper Coal Measures: Turner, Lawrence, near Topeka, Kans. 



Four representatives of this species were found at station 2341 (Scotch Creek) in 

 the Rico formation, and it seems to be fairly abundant there. This material has 

 been compared with the tynes of Meek and Hayden's species and the identification 



