SUBCARBONIFEROUS TERIOD. 83 



one-half of another shown by the specimen bearing such proportionate 

 numbers. The appearance of branching of the arms begins below the 

 periphery of the body, where, starting as if for simj^le pairs, they almost 

 immediately bifurcate, the two inner branches of the two pairs thus foj-med 

 again bifurcating at or just beyond the periphery, the two outer branches 

 of each original pair remaining simple. Surface of the body-plates marked 

 by shai-p, radiating ridges, which give the whole surface below the anus a 

 confused, cancellated appearance. 



Breadth of the body at its periphery, about eighteen millimeters. 



The body of this species resembles in general aspect that of A. prohos- 

 cidialis Hall, and also that of A. asperimus Meek and Worthen, both from 

 the Subcarboniferous limestone at Burlington, Iowa; but it differs from both 

 in shape, in its more delicate surface-ornamentation, and in the different 

 character and branching of the anus. 



Position and locality. — Strata of the Subcarboniferous period ; Mountain 

 Spring, old Moiinon road, Nevada. 



MOLLUSCA. 



MOLLUSCOIDEA. 



Class BRACHIOPODA. 



Order ARTHROPOMATA. 

 Family PRODUCTID^. 



Genus PRODUCTUS Sowerbj^, 1812. 



Productus parvus Meek and Worthen. 

 Plate V, fig. e a and b. 

 Productus parvus Meek and Wortben, 1866, Geol. Surv. of Illinois, ii, 297. 



Shell small, subhemispherical, length and breadth about equal ; length 

 of hinge-line neai-ly or quite equal to the greatest breadth of the shell ; 

 margin regularly rounded from ear to ear by the convexity of the shell. 



Ventral valve regularly convex, without central flattening or mesial 



