Cincinnatian and Lexington Fossils 71 



Pterinea (Caritodens) demissa, Conrad. 



(Plate I, lig. 10.) 



Pterinea demissa, Conrad, as identified from the Cincinnatian 

 strata of Ohio, Indiana, and Kentucky, differs from Pterinea laevis, 

 the type of the genus, in the absence of a well defined, longitudinally 

 striated ligamental area. Along the hinge line, a narrow linear 

 portion is bent parallel to the general plane of the valves, and then 

 inward along the margin, serving as an area of attachment of the 

 valves but without any ligamental thickening or striation. No an- 

 terior cardinal teeth have been seen. The anterior muscular scar 

 must be faint, since it has escaped detection so far. Agreeing with 

 Pterinea are the greater convexity of the left valve, the low con- 

 vexity of the right valve, becoming flat or slightly concave vent- 

 rally in mature shells, the well developed ear and wing, and the 

 obliquity of the body. The posterior muscular scar is large, but 

 not sharply impressed. 



In the Whitewater bed. west of Camden, Ohio, the cast of both 

 valves is marked along the line of junction between the body and 

 the wing by a deep groove, 12 mm. in length in specimens 55 mm. 

 high. These grooves indicate the presence of a single prominent 

 linear posterior tooth in each valve. A similar specimen was found 

 in the Hitz layer, at the top of the Saluda bed, at Madison. Indiana. 

 Careful search among the numerous specimens of Pterinea demissa 

 in the Arnheim and W'aynesville beds has failed to reveal similar 

 posterior teeth on well exposed interiors, nor have any been found 

 in specimens from the Maysville formation. Possibly the White- 

 water forms here described belong to a different species. 



Pterinea demissa appears to be a distinctly more primitive 

 type than Pterinea laevis. This is true especially of the Maysville 

 and lower Richmond forms in which the posterior lateral teeth ap- 

 pear to be absent. These earlier forms are here chosen as the type 

 of the more primitive group for which the term Caritodens is 

 proposed. 



A valve from the Arnheim bed at Clifton, Tennessee (Plate I, 

 fig. 10) is identified with Pterinea demissa. 



Conocardium richmondensis, sp. nov, 



(Plate II, figs. 21 A,B.) 



Shell sub-trigonal ; hinge-line straight ; beaks apparently 



