50 BRACHIOPODS. 



mian fossils (Dyas ), the external difference between this genus 

 and Strophalosia will be at once seen, the latter genus having 

 a cardinal area. The presence of an area alone, however, is 

 not always a sufficient distinction, since there is, in some very 

 rare instances, an abnormally developed area in true Productus. 

 The total absence of cardinal teeth and sockets, however, in 

 the latter genus, clearly separates these types. That P. nebras- 

 censis is entirely destitute of any traces of hinge teeth is well 

 known to all who have examined the interior of this shell. 



Productus semireticulatus (MARTIN). 



Plate xxx vi, figs. 4a-c. 



Productus semireticulatus Martin, 1809 : Petref. Derb., p. 7, pi. xxxii, figs. 



1, 2; pi. xxxiii, fig. 4. 

 Productus semireticulatus DeKoninck, 1844: Monog. Gen. Productua, pi. 8, 



fig. 1. 

 Productus calhounianus Swallow, 185vS : Trans. St. Louis A.ead. Sci., vol. 



I, p. 181. 

 Productus magnicostatus Swallow, 1860: Trans. St. Louis Acad. Sci., vol. 



I, p. 641. 

 Productus semireticulatus Meek. 1872: U. S. Geol. Sur. Nebraska, p. 160, 



pi. v, figs. 7a-b. 

 Productus semireticulatus White, 1875: U. S. Geog. Sur. w. 100 Merid , vol. 



IV, pt. ii, p. Ill, pi. viii, figs. la-c. 



Shell rather large, wider than long; hinge-line equal to 

 greatest breadth of valves. Ventral valve very convex, 

 strongly incurved, with a broad, rounded, mesial sinus ; beak 

 prominent, closely incurved ; ears well defined. Dorsal valve 

 flattened more or less, curved toward the anterior margin. 

 Surface of both valves marked by strong, rounded, radiating 

 ribs, some of which bifurcate ; in the visceral region these are 

 crossed by many concentric folds. Spines stout, few and 

 scattered. 



Horizon and localities- Upper Carboniferous. Upper Coal 

 Measures: Creighton (Oass county), Calhoun ( Henry county). 



