280 PALEONTOLOGY OF ILLINOIS. 



which condition the pores probably appear larger than natural. 

 In specimens with the tumid portion of these plates unremoved, 

 the pores are not readily seen, and the whole dorsal side then 

 seems to be made up of solid, close-fitting pieces. Greatest 

 diameter across between the extremities of the opposite rays, 

 about 2.37 inches; diameter of disc, 1 inch; breadth of ambu- 

 lacral furrows, about 0.10 inch; length of little flattened mar- 

 ginal spines, near 0.08 inch. 



Locality and position: St. Clair county, Illinois; in the St. Louis division 

 of the Subcarboniferous series. 



MOLLUSCA. 



BRACHIOPODA. 



Genus PRODUCTUS, Sowerby, 1814. 



(Min. Conch., tab. 68.) 



Productus scitulus, M. and W. 



PL 20, figs. 5 a, 5 b, 5 c, 5 d. 



Productus scitulus, Meek and Worthen, October, 1860. Proceedings Acad. Nat. Sci., 

 Philad., p. 451. 



Shell small, gibbous, wider than long, measuring from the 

 hinge to the anterior curve ; hinge line rather more than 

 equaling the breadth of the central part of the valves ; ante- 

 rior side rounded, or sometimes a little flattened along the mid- 

 dle; sides rounding to the front, and straight or somewhat 

 contracted near the ears. Ventral valve very gibbous, and 

 rather strongly arched, moderately produced in front, and pre- 

 senting but slight indications of a mesial sinus; ears triangu- 

 lar, convex, or somewhat vaulted, sloping up to the convex 

 visceral region, but separated from the swell of the umbo by a 

 rounded depression; umbo convex, incurved, so as to bring its 

 apex apparently a little beyond the hinge line ; surface marked 



