Cinciiiiiatiaii and Lexington Fossils 51 



margin, chiefly by the intercalation of additional plications toward 

 the anterior marg-in. The cardinal extremities are compressed ver- 

 tically, and the lateral margin forms an angle of about 85 degrees 

 with the hinge line. The sides of the ventral valve are somewhat 

 flattened, and the middle is a little depressed toward the front. 

 The area of this vah-e is only moderately inclined backward. 



As a matter of fact, several of the specimens in this series of 

 types undoubtedly belong to Plcctorthis ncglccta. These are the 

 specimens which have given rise to the following parts of the 

 original description : 



Cardinal extremities usually truncate or rounded: Dorsal valve convex, 

 becoming gibbous, with a shallow often scarcely defined sinuosity in the middle; 

 middle of the ventral valve sometimes a little depressed towards the front. 



Occasionally Plccforfhis ncglccta is distinctly sinuous along 

 the anterior margin, due to a slight elevation along- the median 

 parts of the brachial valve, anteriorly, and to a corresponding flat- 

 tening or depression of the pedicel valve. This inclusion of typical 

 specimens of Plcctorthis ncglccta among the types of Plcctorthis 

 janicsi suggests either that the type of Plcctorthis dichotoma was 

 lost as long ago as i86t, or that the latter species was not identical 

 with Plcctorthis ncglccta. 



Associated widi these specimens of the Plcctorthis ncglccta 

 type, in this series of types described as Plcctorthis janicsi, are a 

 number of smaller specimens, which seem to have been regarded as 

 the young of Plcctorthis /anicsi, and to have inspired the following- 

 parts of the original description : 



Often the striae are si)u/^lc throughouf. and. when well preserved, are 

 always marked by fine thread-like concentric striae, and towards the mar- 

 gin by a few lamellae of growth; this species in general form, resembles 

 Orthis l^licatella; but the area is much larger, and extends to the salient 

 cardinal extremities; while in that species the extremities are usually 

 rounded and the shell a little rounded below. 



These smaller sjiecimens belong in the Corryville bed. 100 

 feet above the Plcctorthis ncglccta horizon. Local collectors at 

 Cincinnati have usually regarded these smaller specimens as 

 the true tvpes of Plcstorthis janicsi, notwithstanding the faci 

 that they are described in the second and third paragraphs 

 of the original description, while the large specimen figured 

 by Hall and Whitfield and the specimens of Plcctorthis nc- 

 glccta, already mentioned as occurring among the series of 

 types, formed the basis of the first ])arag-raph of the description. 

 Plcctorthis ncglccta is found in the Mount Hope bed, but very 



