44() CARBONIFEROUS FORMATIONS AN1> KAITNAS OK COLORAOO. 



Ill shape (liis I'driu rcsi'inhlcs that idiMitiHcd as PI. Kidicostatii-'^^ hut it is a l«ss 

 oli)n,i>iU(> shell, the anterior portion is a trifle nion; prominent, and it lacks the 

 riuliatiiii;- ril)s which ci'oss the upper and posterior half of shells of that species. 



'I'his form seems to be of the type of PI. angulatun., but differs in lieing nnicli 

 larger and proportionately less transverse, in having the anterior end slightly less 

 produced, and the antei-ior muscular scar more deeply marked. 



Local if !/ (Old horizon.. — Grand River region, below mouth of canj'on of Eagle 

 River (station 2192); base of Weber formation. 



Pleurophorus occidentalis Meek and Hayden ? 



18.58. Heuwpliovus occidcntalis. Meek and Hayden, Albany Inst., Trans., vol. 4, p. 80. 



Permian: In Nebraska, on Missouri, opposite north Missouri boundary. 

 1859. Pleurophorus occidenkdis. Shumard, Acad. Sci. St. Louis, Trans., vol. 1, p. 396. 



Wliite Permian limestone: Guadalupe Mountains. 

 1864. Plcuropliorus occidentaiis. Meek and Hayden, Smithsonian Cont. Knowledge, vol. 14, No. 172, 

 p. 35, pi. 1, figs. 11a, b. 



Coal jNIeasures: Nebraska, nearly opposite northern boundary of Missouri. 

 1866. CUdophorxis palkm. Geinitz, Carb. und Dyas in Nebraska, p. 23, tab. 2, fig 3, 4. CSot Mytihis 

 ■pallad deY em., lS4o.) 



Upper Coal Measures: Nebraska City, Nebr., light gray limestone of Wyoming, 7 mile.s north 

 of Nebraska City. 

 1866. Clidophorus occidental^. Geinitz, Carb. und Dyas in Nebraska, p. 23, pi. 2, fig. 6. 



Upper Coal Measures: Stage C. c"', Nebraska City, Nebr. 

 1872. Pleurophorus ocmdentalisf Meek, U. S. Cieol. Surv. Nebraska, p. 212, pi. 10, fig. 12. 



Upper Coal Measures: Otoe City, Nebr.; Nebraska City, Nebr.; Grayville, 111. 

 1891. Clidophorus occidenlalis. AVhite, U. S. Geol. Surv., Bull. No. 77, p. 27, pi. 4, fig. 3. 



Permian: Goodwin Creek, Baylor County, Tex. 



Of this form but a single not too perfect example has come to hand, and it is 

 identified with some doubt. It is small, with a Avidth of about 11 mm. and a height 

 somewhat less than half as great. The general shape much resembles the Nebraska 

 shell which Meek figures as PI. occidentals, and with that species 1 have provisionally 

 identified it. The dorsal and ventral margins are nearty straight and converge some- 

 what anteriorly. The posterior end is rather evenl^^ rounded. The umbones are so 

 much inclined forward that they project nearly as far as the small anterior portion. 

 The curvature is regular, and there is no distinct umbonal ridge. About halfwa}' 

 between the cardinal line and a diagonal joining the anterior superior and posterior 

 inferior angles there is a well-marked radial rib, with possibly traces of one or two 

 others below (?). The surface is marked by verj^ tine concentric striae. 



The cardinal edge is angulated as in the shell referred to PI. suicostatua, so that 

 a narrow strip of shell along the hinge line is horizontal when the valve is viewed 

 from above. 



Probably with this species belongs a ver}^ imperfect specimen from the Lead 



