Cincinnatian and Lexington Fossils 6r 



moderately ele\atecl. and is marked by four plications, two of which 

 bifurcate anteriorly, but this is only an individual characteristic. 

 As a rule, shells of this species have only four simple plications on 

 the fold. Three plications occur in the sinus. The type (plate 

 VI, figs. II A.E) is also abnormal in presenting an exceptionally 

 short hinge-line. 



Most specimens of Platystrophia morroiuensis, as here inter- 

 preted, differ from the type of the species in having a distinctly 

 longer hinge-line, frequently equalling four-fifths of the width of 

 the shell. To specimens of this character, Ulrich gave the cata- 

 logue name, Platystrophia siniilis. Ulrich's specimens were secured 

 15 feet below the top of the Corryville bed. at Cincinnati. Ohio. 



The very low^ broad fold, and short hinge-line suggest young 

 specimens of Platystrophia ponderosa, a much larger species occur- 

 ring in the Mount Auburn bed. 15 feet higher. In Platystrophia 

 ponderosa, however, the two primar}^ plications on the fold are 

 distinctly more conspicuous than the secondary plications within 

 7 mm. of the beak, and the two secondary plications are arlded at 

 a distinctly lower level, at a distance of 3 or 4 mm. from the beak, 

 while at this distance, those of Platystrophia morroivensis are 

 already distinctly differentiated and lie very nearly at the same level. 

 Moreover, all of the plications of Platystrophia morrowensis are 

 sharper and more distinct than any specimens of Platystrophia 

 ponderosa of the same size. 



Platystrophia cypha, James. 



(Plate IV. iig. Jo A.B; Plate V, fig. ii.) 



The type specimen possessed the following characteristics : 

 Shell elongated along the hinge-line into spine-like projections, 

 being over two-thirds wider here than across the center of the shell, 

 as is indicated by the following measurements. \\^idth along the 

 hinge-line, one and a half inches; width half \vay below the hinge- 

 line, less than an inch ; length, three-quarters of an inch. Shell 

 extremely gibbous, the convexity equalling the width of the body 

 below the spine-like projections. Brachial valve with a remark- 

 ably elevated median fold whose flanks form an angle of about 80 

 degrees with the sides of the shell. Pedicel valve with a profound 

 sinus. Sinus with one strong elevated plication in the center and 

 an obscure elementary one on each side. Fold with tw^o strong 

 plications on the crest, and although no obscure rudimentary plica- 



