350 Report of the State Geologist. 



Derbya (?) biloba. 



Plate 5, figs. 17, 18. 



Derhya {?) biloha, Hall. Palaeontology of N. Y., vol. VIII, pt. 1. p. 350, pi. xi, 

 figs. 4, 5. 1893. 



Shell small, obcordate in outline. Hinge-line short and 

 straight, its length being considerably less than one-half the 

 width of the shell. On the pedicle-valve the cardinal area is 

 moderately high and slightly arched backward; delthyrium 

 covered. The surface of the valve is somewhat depressed or 

 flattened over the pallial region. The brachial is deeper and 

 more convex , the umbo is full but not elevated, and just in front 

 of the apex there begins a broad and conspicuous sinus which 

 widens rapidly and renders the shell bilobate on its anterior 

 margin. 



Surface covered with numerous fine radiating striaB. Interior 

 unknown. 



Upper Coal Measures. Winterset, Iowa. 



Streptorhynchus Ulrichi. 



Plate 6, fig. 3. 

 Streptorhynchus Ulrichi, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, p. 

 351, pi. xib, fig. 15. 1892. 



Shell of comparatively large size for this genus. G-eneral con- 

 tour subtrihedral. Hinge-line shorter than the greatest diameter 

 of the valves. Cardinal area high, somewhat incurved and dis- 

 torted ; sides considerably shorter than the base. Deltidium 

 broad. Marginal outline of the pedicle-valve, from hinge-line 

 forward, semiovate, somewhat irregular, contracted toward the 

 hinge and expanding in the pallial region. The interior of the 

 pedicle-valve shows strong teeth, the dental lamellaD extending 

 downward and inclosing the posterior portion of an ovate mus- 

 cular scar. There is no median septum. External surface con- 

 vex in the upper part, becoming depressed toward the anterior 

 margin ; quite irregular in growth, being crossed by more or less 

 conspicuous concentric ridges or varices ; covered with numerous 

 fine radiating, subequal striae, which increase by implantation. 

 Brachial valve not known. 



Chester limestone. Crittenden county, Kentucky. 



