458 DESCRIPTIONS Or NEW SPECIES OF FOSSILS FROM THE 



Surface mai-ked by comi3aratively strong, radiating stria^, which are sometimes 

 continuous, at other times intei-ruiited, then having the appearance of very elongate 

 pustules ; at the base about six in the space of 5 mm. 'No concentric striie have 

 been observed, though it is possible that they exist on more perfectly preserved 

 specimens. 



A typical specimen measures as follows : "Width at the base 30 mm. ; thickness 

 20 mm. ; height 30 mm. ; width of sides equal ; width of i-idges <mi posterior side 

 3 mm. ; of depressions slightly more ; of carina 3 mm. 



This form resembles the two specimens which are figured in the Pal. of New 

 York, Vol. V, Pt. II, PI. I, Figs. 20-23, which differ materially from the other figured 

 specimens placed under that species. The ether specimens, though perfectly pre- 

 served and showing concentric striae, have no indication of radiating strife, while in 

 the specimens described they are one of the most characteristic features ; they are 

 also shown in the figures mentioned above. The plications are also stronger and the 

 form more regularly conical. 



This species resembles P. striatum from this formation, but may be easily distin- 

 guished by its straight form, the equal length of the sides, the coarser striations, and 

 the strong plications of the posterior sides ; from P. hreve it is distinguished by its 

 more elongate form, oval aperture, more continuous radiating strije, and the conspic- 

 uous plications of the posterior side. 



Formation and locality. Chemung group, four miles north-west of Warren, 

 Warren county, Pennsylvania. 



PLATYCERAS VAEIANS Simpson, n. sp., Fig. 28. 



Shell small, subconical, curved, slightly oblique; apex not incurved or bent; 

 width at the base two-thirds the length of the anterior side, and about equal to the 

 posterior. 



Plications frequent, variable in number. On the dorsum there is sometimes a 

 faint indication of a carina; on the left side is a deep conspicuous furrow, which ex- 

 viiig. tends about thi'ee-fourths the length of the shell from the base; beyond 

 this there is a slighter furi'ow ; the area between them elevated, 

 I'ounded and very prominent. On the posterior side of the shell are 

 usually two or three slight furrows, but occasionally a stronger one, and 

 ""iBBm on the left side there is one nearly as strong as on the opposite side. 

 Sometimes on the posterior side the ai'ea between two of the smaller furrows is ele- 

 vated, having the ajipearance of a ridge or carina, which is occasionally prominent. 



