Cincimialiaii and Lexington Fossils 63 



Shells belonging to the opposite extremity of the series, with 

 the postero-lateral angles almost rectangular, with only 5 or 6 

 lateral plications, and with the lateral plications on the fold and 

 on the walls of the sinus almost or endrely obsolete, form the 

 PlafystropJiia nnicosfata of Cumings. (Plate IV, fig. 6.) 



Between these extremes belongs the larger series with only a 

 moderate extension along the hinge-line, with 6 to 8 lateral plica- 

 tions on each side of the fold, and with the lateral plications of the 

 fold and sinus more frequently present, though inconspicuous. 



All the variants of Plafystrophia cypha have been found in 

 the upper part of the rich Platystrophia ponder osa beds at the 

 Bellevue horizon, and in the overlying Corryville beds at Madison, 

 Mount Sterling (plate IV, fig. 12 A,B), Vevay, and Xew Hope 

 church in Ohio county, in Indiana. This may have been the hori- 

 zon also at which James collected his type specimens in Warren 

 county. Ohio. 



Cumings has pointed out the probable derivation of Platystro- 

 phia iniicostata from Platystrophia laticosta of the Fairmount bed. 

 The later developments of Platystrophia cypha also are of interest. 



If emphasis be laid on the prominence of the fold, the depth of 

 the sinus, the tendency toward prolongation along the hinge-line, 

 and the inconspicuous size and low position of the lateral plicacions 

 of the fold rather than their absence, then the descendants of 

 Platystrophia cypha can be recognized readily in the .\rnheim. 

 For instance, one mile south of Mount \\'ashingi:on, and a mile 

 south of Smithville, on the road from Louisville to Bardstown; 

 near Lebanon; three miles south of Maysville, Kentucky (plate iii, 

 fig. 5). Also three miles northeast of Goshen in Clermont county, 

 and at Oregonia in Warren county. At the locality one mile south 

 of Mount Washington, Kentucky, specimens wdth spine-like pro- 

 longations along the hinge-line were found which agree with 

 James's original description better than does the best of his series 

 of type specimens. 



A somewhat similar group of specimens occurs in the W^aynes- 

 ville bed. In this group, the lateral plications on the fold some- 

 times are inconspicuous and situated low on the flanks, but more 

 frec|uently they are farther up the sides of the flanks and tend to 

 be more conspicuous than in the case of shells from lower horizons. 

 Shells of this type occur in the ^^'aynesville at Madison, and Ver- 

 sailles, Indiana, at Oregonia, and Clarksville, Ohio, and at Con- 



