730 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



foramen in perfect adult shells. Dorsal valve convex ; greatest convexity 

 near the umbo, from which it slopes gradually to the lateral and antero- 

 lateral margins. Mesial fold confined to anterior half, broad and high 

 in front, and divided in the middle by a wide, longitudinal, subangular 

 furrow ; rudimentary furrows on either side of the middle. Both valves 

 with three or four plications on either side of mesial fold and sinus in 

 adult shells 5 plications confined to antero-lateral margins. Postero- 

 lateral margins and umbonal region smooth. Shell thin, translucent, 

 scarcely fibrous. 



Dimensions of a large specimen are: Length, 28; width, 41; thick- 

 ness, 23 millimeters. 



Confined, as far as known, to the dark shales at Independence. 



Gypidula munda, n. s. 



Shell small, subtriangular to broadly ovate, inequivalve; ventral 

 valve convex, curving almost regularly from beak to front margin; 

 beak only moderately prominent, obtuse, slightly incurved ; an indis- 

 tinct mesial fold near the front margin. Dorsal valve transverse ellip- 

 tical in outline, slightly convex near the beak, sloping at first somewhat 

 abruptly and then more gradually toward the cardinolateral margins; 

 a broad sinus, of which the middle is occupied by a single low fold, is 

 confined to the anterior margin. A few indistinct folds occupy the 

 antero-lateral margins of both valves; surface otherwise smooth. 



Area and foramen as in other species of this genus. 



Length, 8 ; width, 10 ; thickness, G millimeters. 



This species resembles Gypidula occidentalism Hall, from which it may 

 be distinguished by its smaller size, less i)rominent beak, greater pro- 

 portionate width, and deeper sinus. The young G. occidentalis of corre- 

 sponding size are entirely smooth, and show no trace of either fold or 

 sinus. They differ also from G. munda in form and general proportions. 



From the dark shale at Independence. The species is unknown from 

 any other horizon. 



Productus (Productella) dissimilis, Hall. 



Produetus dissimilis, Hall, Geology of Iowa, 185S, vol. i, part 2, p. 497, plate iii, fig. 

 7 a~G. 



This species is abundant at Rockford, and is among the most common 

 species in the Independence shales. 



Productus (Productella) sp.? 



The collections from the Lower Devonian Shales contain a few speci- 

 mens of this small Productus. It is somewhat related to P. Shumardianus, 

 Hall. More material will be necessary before it can be determined. 



