266 PROCEEDINGS OF THE ACADEMY OF 



face of the shell is prohahly also marked with more or less distinct lines of 

 growth. The internal casts show very satisfactorily the muscular scars. 



This species has somewhat the general form of P. Jissurella, of Hall, hut 

 is smaller, less oblique, and differs in the possession of large radiating 

 plications. 



Locality and position same as last. 



Platyceras (Oethoxychia) ixfcndibcluji, M. & W. 



Platyceras subrectum, Hall, 1S60. Supplement to Iowa Report, page 1, of 



additional sheet; (not P. subrectum, Hall, 1859. Twelfth Report Regents 



Univ., N. Y., p. 18.) 



Shell straight, more or less elongate-conical, very slightly oblique, attenuate 

 near the straight subcentral apex, thence expanding, at first gradually, then 

 more rapidly to the irregularly subcircular or suboval aperture ; lip thin and 

 irregularly undulated, as if to correspond to an uneven surface of attachment. 

 Surface with more or less distinct, undulating, concentric striae, and near the 

 lip stronger marks or lamina? of growth; also generally with a few large, 

 irregular, undefined, radiating plications. 



Length. 1*40 inch ; breadth about l - 30 inch. 



As remarked hy Prof. Hall, this species varies considerably in the degree of 

 expansion, some specimens being much more attenuated than others. It is 

 probable that in very young individuals the immediate apex may have been 

 curved or subspiral, but in all those we have seen it is straight, sometimes a 

 little compressed, and only removed from a central position by the slight 

 general obliquity of the whole shell without any curve. In some respects it 

 is similar to P. quincyense, of McChesney, from the Burlington division of the 

 Subcarboniferous series. It differs, however, even when, as is sometimes the 

 case, it is nearly as strongly plicated as that shell, in its more irregular, less 

 attenuate form and rougher surface, as well as in not having its folds or pli- 

 cations forming five regular, broad ridges, more or less flattened and concave 

 along their middle. 



From P. fisnurella, Hall, the shell here described differs in being less de- 

 pressed or more attenuate, particularly near the apex, which is never oblique 

 as in that species. 



Prof. Hall hail described the species under consideration, in the supplemen- 

 tary skeet quoted above, but as he by an oversight gave it the same specific 

 name {subrectum) he had previously applied to another species froui the upper 

 Heidelberg rocks of New York, it becomes necessary, in order to prevent con- 

 fusion, that our Illinois species should receive another name, and hence we 

 propose to call it P. infundibulum. 



From the same locality and position with the above, we have a single speci- 

 men differing from the others in bein<_ v greatly more slender and elongated. It 

 is perfectly straight, somewhat compressed laterally and about twice as long 

 as wide, being very attenuate above the middle and but slightly expanded be- 

 low. It is an internal cast, showing no surface markings, but preserving the 

 transversely elongate-oval muscular scar on each side, apparently connected 

 by a slender band behind. It is not possible to determine beyond doubt 

 whether this is a distinct species or only a variety of that described above, 

 without having more specimens for comparison. Should it prove distinct, 

 however, we would propose to call it Platyceras (Orthonyckia) extinctor, in 

 allusion to its resemblance in form* to a candle extinguisher. 



Locality a n<l jiusition. Keokuk division of the Subcarboniferous series, 

 Warsaw, Illinois. 



Genus METOPTOMA, Phillips, 183G. 



From Phillips's figures, and very brief diagnosis of the genu? Metoptoma,* it 



* " Patcllifurrn, face under the apex truncate." Qeol. Yoiks, 11, p. 223. 



[July, 



