52 Aug. F. Focrste 



similar specimens occur in the lower Corryville east of Maineville, 

 in Warren county, Ohio. It is possible that the large figured speci- 

 men also is a Corryville form. Its chief feature is the extended 

 width of the shell along the hinge-line, the postero-lateral angles 

 equalling about 85 degrees. In other respects the shell resembles 

 some of the forms of Plectorthis found in the Fairmount bed (plate 

 VI. fig. 2). 



Plectorthis neglecta, James. 



(Plate VI, figs. I A-E.) 



Figure 21, plate V, of the Nczv York Paleontology, vol. VIII, 

 labelled Plectorthis dichotoma, is the interior of the Mount Hope 

 species, Plectorthis neglecta, James. 



The types of Plectorthis neglecta, numbered 2399. are pre- 

 served in the James collection, in Walker Museum at Chicago 

 University. In this species the intercalation of secondary plica- 

 tions often begins within 3 or 4 mm. from the beak and additional 

 plications may be added near the anterior margin. The secondary 

 plications soon attain about the same height and width as the 

 primary plications, so that the shell in general has a more closely and 

 uniformly plicated appearance than any other species of Plectorthis 

 found near Cincinnati. The grooves between the primary and 

 secondary plications are narrow^ Not infrequently the anterior 

 half of the pedicel valve is slightly depressed or flattened. 



Plectorthis neglecta makes its appearance in the Mount Hope 

 bed, at Cincinnati, and extends at the same horizon southwest ward 

 to Vevay, Indiana, and southward to Mason, Kentucky. It distinctly 

 precedes Plectorthis pUcatella of the Fairmount, and must belong to 

 a different line of descent. 



Plectorthis dichotoma may be identical with Plectorthis neg- 

 lecta, but in the absence of the type and in the presence of the 

 figure accompanying the original illustration, this appears doubt- 

 ful. It is unfortunate that among the numerous types in the Hall 

 collection, the apparently aberrant types, Plectorthis eqnivalvis and 

 Plectorthis dichotoma, should be missing or at least not definitely 

 identified in the collections as types of these species. Under these 

 conditions it might be preferable to abandon the doubtful term 

 Plectorthis dichotoma for the definite one Plectorthis neglecta. 

 Hebertella sinuata, Hall. 



(Plate II, fig. 5-) * 



Hebertella sinuata differs from Hebertella occidentalis chiefly 

 in the absence of the slight median depression near the beak of 



