DESCBIPTIONS OF SPECIES. 373 



strong, mesial depression. The visceral area is but slightly convex. After attain- 

 ing a length of about 15 mm. the shell assumed a strong downward growth, so that 

 the peripheral portion lies almost perpendicular to the plane of the viscei'al area. 

 The surface is crossed bj' rather coarse radiating stria;, 10 or 12 in the space of 10 

 mm., and the entire visceral portion is traversed by fine concentric wrinkles. 



In size the shell corresponds to Productufi sp. h, but is much more coarsely 

 striate. It resembles in striation as well as shape both P. semireticulatus var. her- 

 rnosanus and Marginifera muricata^ but is much smaller than the one and much larger 

 than the other. 



We have two authentic specimens of M. lasallensis from Lasalle, 111., with which 

 collections from Pawnee City, Nebr., Fort Scott, Kans., and Graham, Young County, 

 Tex., agree in every way. The collections from Kansas, Nebraska, and Texas I do 

 not hesitate to refer to the same species as the shell from Illinois which Worthen 

 has identified as 31. Imallensis. These specimens, however, do not agree with 

 Worthen's figures and description in several particulars. He states that M. lasallen- 

 sis is without concentric wrinkles over the po.sterior portion of the shell, a character 

 which all these specimens possess in some degree, and which is usually well marked. 

 Furthermore, he has restored his fragmentarj' specimen in such a manner as to make 

 a larger shell than anj' seen by me, and to give it a very alate shape, while the hinge 

 line of the specimens I have studied is but little extended. 



The Colorado examples present a close superficial agreement with this, as I 

 regard it, characteristic material, but the true Productus lasallensis clearly belongs 

 to Waagen's genus Marginifenxi^ while I doubt if my material does. Still, the latter 

 is too imperfect to permit me to satisfy myself upon this point. Were it not for 

 this important difierence I would refer the Coloi'ado specimens without hesitation to 

 Worthen's species, so close is their general agreement. 



Locality and ho7'izmi. — Crested Butte district (station 2316?); Weber limestone. 



Maeginifera muricata Norwood and Pratten. 



PI. V, figs. 5, .5b, 6, 6b, 7. 



? 1852. Produclus flemingii. Roemer (non de Koninck), Kried. von Texas, p. 89, pi. 11, figs. 8a, b. 



Carboniferous: San Saba Valley, Texas. 

 1855. Produclus niuricatus. Norwood and Pratten, Acad. Nat. Sci. Philadelphia, Jour., (2), vol. 3, 

 p. 14, pi. 1, figs. 8a-e. (Not P. mMricato Phillips. ) 

 Coal Measures: Fishhook Creek, Pike County, 111. ; 6 miles northwest of Richmond, Mo. 

 1857. Productus muricatus. Cox, Geol. Surv. Kentucky, Rept., vol. 3, p. 573, pi. 9, fig. 6. 



Coal Measures: Union County, 111.; Lewisport, Hancock County, Ky. ; Gallatin County, III. 



1876. Produclus muricatus. White, Powell's Rept. Geol. Uinta Mountains, p. 90. 

 Lower Aubrey group: Near Echo Park, Utah. 



1877. Produclus muricatus. White, U. S. Geog. Geol. Surv. W. 100th Mer., Rept., vol. 4, p. 120, pi. 8, 



figs. 4a-c. 

 Carboniferous. Rock Creek, Lake County, Colo. 



