Cincinnatian and Lexington Fossils 29 



defined, the term Sunset bed has been selected. This bed is well 

 exposed southwest of Sunset, in Fleming county, on the road to 

 Day's Mill. It contains occasional specimens of Platystrophia pon- 

 derosa. It is well exposed also at Wyoming, in Fleming county,, 

 where the base of the immediately overlying fossiliferous section 

 contains Leptacna richmondensis-precursor, and Rhynchotrema 

 dcnfata-ornlicinicnsis. 



Rhynchotrema dentata, Hall. 



(Plate II, fig. 16; Plate III, fig. J2.) 



Rhynochotycuia dentata, as represented in the upper part of the 

 Whitewater bed. at Richmond, Indiana (plate III, fig. 12), is 

 characterized by the greater convexity of both valves. The middle 

 part of the pedicel valve usually is not flattened and then partly 

 reflexed toward the anterolateral angles, as is more frequently the 

 case in large specimens of the Arnheim variety. 



Zygospira modesta, Hall. 



(Plate II, fig. 15 A,B.) 



The type specimen, numbered 1 356-1, preserved in the Amer- 

 ican Museum of Natural History in New York City, is 7.8 mm. 

 long, 9.2 mm. wide, and 4.1 mm. thick. The pedicel valve has 18 

 distinct plications, and two indistinct ones, the latter being near the 

 hinge margin. The four median plications are moderately elevated 

 above the general convexity of the shell, and form a rather low, 

 median elevation. The groove along the median line of this eleva- 

 tion is conspicuously wider than the two adjacent grooves. Cor- 

 responding to the median groove, the brachial valve has a com- 

 paratively strong median plication, while the two adjacent plica- 

 tions, one on each side, are distinctly narrower. A broad, but com- 

 paratively shallow depression extends from near the beak to the 

 anterior margin of the shell; its lateral borders are not sharply 

 defined but are formed approximately by the third plication on each 

 side of the median plication. The specimen evidently was found 

 in Cincinnatian rocks ; it is labelled as coming from Cincinnati, 

 Ohio, but this may mean merely that the specimen was obtained 

 from some Cincinnati collection. 



Similar specimens are found in the Fairmount bed at Cincin- 



