372 CARBONIFEBOUS FORMATIONS AND FAUNAS OF COLORADO. 



Productus sp. a. 



PI. V, litr. :i 



This species has ii vory .scanty representation jinionij- our collections, four frag- 

 mentary specimens from three localities in the San Juan region, being all the material 

 that has so far come to hand, '.rhe shape of the ventral valve appears to be not 

 unlike that of P. semiretievlatvN var. hermomnim^ but the beak is as a rule more 

 tapering. There is a more or less distinct siiuis. The posterior portion is crossed 

 by rather faint, irregulai' wrinkles. The striis are sharp but nodulcse, and some- 

 what discontinuous, especially al)out the ears. They thus present a wavy, irregular 

 appeai'ance. The nodules formed in many cases the bases of small spines. 



The dorsal valve is more regular arid finely reticulated, the spaces between the 

 striae and wrinkles forming little pits. 



At one time I was disposed to place this form with that which Marcou identified 

 as P. jn/xidati(x de Koninck, but this course seems hardly prudent in view of his 

 rather meager, poor, and conflicting figures and description. 



There can be no doubt that his identification with de Koninck's .species, if his 

 figures even approach accuracy, is altogether incorrect. 



Locality and hoi-izon. — San Juan region (stations 2208, 2328, 2336); middle and 

 upper portions of the Hermosa formation. 



MARGINIFERA Waagen, 188i. 

 Marginifera lasallensis Worthen?. 



PL V, figs. 4-4a. 



1873. Productus lasallensis. Worthen, Geol. Snrv. Illinois, Kept., vol. 5, p. 569, pi. 2.5, fig. 9. 



Upper Coal Measures: Lasalle, 111. 

 1892. Productus (Marginifera) lasallensis. Hall and Clarke, Int. Study of Brach., pt. 1, pi. 22, 

 fig. 15. 

 Upper Carboniferous: Lasalle, 111. 

 1892. Productus (Marginifera) lasallensis. Hall and Clarke, Pal. New York, vol. 8, pt. 1, pi. 17A, 

 fig. 13. 

 Upper Carboniferous: Lasalle, 111. 



The form which I have referred to Worthen's species is represented b3^ one good 

 dorsal ^'alve and by fragments of three ventrals. The latter are almost too poor to 

 serve for description or as a guide in identifying the species, but the dorsal seems 

 to be identical in its diagnostic characters with the corresponding valve of P. 

 lasallensis. 



Viewed from its convex or inner side this specimen may be described as follows: 

 In shape it is transversely semielliptical, hinge line about 28 mm. long, ears quad- 

 rate, defined by two shallow radiating grooves. There is a distinct, though not ver^^ 



