GASTROPODA. 121 



complete. The characters by which the species of Platyceras are differentiated are so 

 uncertain, at the best, that a close reference is preferable to a new species. Ulrich found 

 an Oriskany Platyceras in the Upper Devonian of Iowa. 1 

 Occurrence — Mineola of Montgomery County. 



Platyceras carinatum Hall 

 Plate 26, figures 10 and 11: 



1879. Platyceras carinatum Hall, Pal. N. Y., V, pt. 2, p. 5, pi. 2, figs. 12-29. 



1901. Platyceras carinatum Kindle, Indiana Dept. Geol. Nat. Res., 25th Ann. Rept. 



pp. 721-722, pi. 18, figs. 5-7. 

 1909. Platyceras carinatum Grabau and Shimer, North American Index Fossils, I, 

 pp. 683-684, fig. 963b. 



Hall's description — "Shell obliquely subconical or subpyramidal; the nucleus or 

 apex minute, and making from one to one and a half volutions which are vertically 

 compressed, and below which the body volution is abruptly expanded; the dorsum 

 angular or marked by an angular carina which often becomes double in old shells, or 

 is rounded on the summit. This angularity or carina indicates, by direction of the 

 striae, the existence of a sinus in the peristome from an early period of growth; and 

 sometimes there may have been two of such sinuosities close together, giving the double 

 carina, with longitudinal folds (obscure plications) on one or both sides, which become 

 more strongly developed toward the aperture, and are very conspicuous in old shells; 

 the right side is more expanded than the left, and in some well-preserved specimens is 

 nearly twice as wide. Aperture very oblique, rhomboidal or subtriangular, and the 

 peristome sinuous. 



Surface marked by fine, closely arranged, undulating striae of growth, which are 

 not lamellose." 



Remarks — Specimens from the Mineola agree with Hall's species in shape and 

 dimensions but as only interior moulds are preserved the identification is somewhat 

 uncertain. 



Occurrence — Mineola limestone of Montgomery and Warren Counties. 



Platyceras conicum Hall 

 Plate 26, figuies 15 and 16. 



1879. Platyceras (Orthonychia) conicum Hall, Pal. N. Y., V, pt. 2, p. 3, pi. 1, figs. 



13-23. 

 1901. Platyceras conicum Kindle, Indiana Dept. Geol. Nat. Res., 25th Ann. Rept., 



pi 721, pi. 18, figs. 2, 2a and 2b. 

 Hall's description — "Shell erect, conical, the minute apex closely incurved. Body 

 volution entirely straight, with broad undefined longitudinal ridges and depressions, 

 which become more distinct toward the aperture; height of the shell a little greater 

 than the width of the aperture, which is a little longer than wide. Surface marked by 

 concentric undulating striae which become sublamellose toward the aperture and are 

 sometimes closely crowded and wrinkled with numerous knots and nodes. Peristome 

 deeply sinuous; the width from the anterior to the posterior side a little greater than the 

 transverse diameter. The length of the shell is one and a half inches or more, with the 

 aperture a little less." 



Remarks — At locality number 4 of the Mineola, this species is abundant but it has 

 not been collected fiom other localities. The apex is missing from all specimens. The 

 specimens agree in detail with some of Hall's and Kindle's figures of the species. The 

 specimen shown in figures 12 and 13 of plate 20 may belong to a different species but 

 part of Hall's description would seem to include this variety. 



iGeol. Surv. 111., Ill, p. 442, 



