418 CAKBONTFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



belonged to a hitherto undescribed genus, pointed out characters which, if not the 

 result of imperfect jireservation. as seems unlikel}', would certainly entitle it to such 

 a position. He says "The only specimens of this species I have seen consist 

 entirely of what seems to be the thin outer layer of the shell, in which there appears 

 to be a prismatic structure, as seen by the aid of the microscope and a strong trans- 

 mitted light. They show no flattened cardinal plate, but a furrow along the inner 

 side of the hinge margin of each valve. The cardinal plate or area was doubtless 

 composed, as in other cases^ of the inner laminated portion of the shell, that has 

 been destroyed during the fossilizing process; if not, it would seem to be a new 

 genus."" 



The very characteristic spines with which Acanthopecten is armed, projecting 

 from the surface and from the margin, are suggestive of a genus to be developed at 

 a much later geologic period, SpondyVm^ in which the spines often play an impor- 

 tant part in the matter of surface ornamentation. 



Acanthopecten carboniferus Stevens. 



1858, Pecien carboniferus. Stevens, Am. Jour. Sci., (2), vol. 25, p. 261. 



Coal Pleasures: Crooked Creek, Marion County, 111. 

 1863. Pecien broadheadii. Swallow, Acad. Sci. St. Louis, Trans., vol. 2, p. 97. 



Upper Coal Measures: Harrison County, Mo. 

 1866. Pecteii hawni. Geinitz, Carb. und Dyas in Nebraska, p. 36, tab. 2, figs. 19a, b 



Coal Measures: Nebraska City, Nebr. 

 1872. Aviculopecleu carboniferus. Meek, U. S. Geol. Surv. Nebraska, p. 193, pi. 4, fig. 8; pi. 9, figs. 4a, b. 



Upper Coal Measures: Nebraska City, Nebr. 



Coal Measures: Iowa; Illinois; West Virginia. 

 1874. Aviculopecten carboniferus. Meek, Am. Jour. Sci., (3), vol. 7, p. 489. 

 1884. Ameulopecten carboniferus. White, Geol. Surv. Indiana, 13th Rept., pt. 2, p. 144, pi. 28, figs. 5-6. 



Coal Measures; Lick Branch, near Silverwood, Fountain County, and in Vermilion County, Ind. 

 1887. Aviculopecten carboniferus. Herrick, Sci. Lab. Denison Univ., Bull., vol 2, p. 67, pi. 3, fig. 13. 



Coal Measures: Flint Ridge, Ohio. 

 1894. Aviculopecten carboniferus. Keyes, Missouri Geol. Surv., vol. 5, p. Ill, pi. 43, figs. 4a, b. 



Upper Coal Measures: Kansas City, Mo. 

 1897. Aviculopecten carboniferus. Smith, Am. Phil, Soc, Proc, vol. 35, p. 33. 



Lower Coal Measures: White and Conway counties, Ark 

 1900. Aviculopecten carboniferus. Beede, Univ. Geol. Surv. Kansas, Rept., vol. 6, p. 117, pi. 13, fig. 9. 



Upper Coal Measures: Kansas City, Turner, Eudora, Lawrence, Lecompton, Topeka,i Kans. 



This strongly characterized species seems to be rai-e in the Colorado Carbonif- 

 erous faunas. It has been found at but few localities, and is represented by no more 

 than a single specimen at each. 



Locality and hm-izon.—'Si&n Juan i-egion (stations 2:i04, 2206, 2226, 2238, 2342); 

 upper portion of the Hermosa formation and in the Rico formation. Leadville 

 region (station 2259). 



atJ. S. Geol. Surv. Nebraska. 1872, p. 194. 



