272 



Fig. 194. Platyceras 

 erection (after Hall). 



Platyceras erectum. Hall. (Fig.ly4.) (Pal.N.Y.,Vol. 



. Pt. II.. p. 5, PI. II.) 



Distinguishing Characters. — Closely in rolled apex, for one 

 and one-half volutions; rapidly expanding 

 lower portion; outer surface regularly 

 arcuate to the inrolled spire; concentric 

 laniellose striae, arched abruptly over nar- 

 row bands, marking former sinuosities in 

 the peristome. 



Found in the Demissa beds, at Section 5 

 (where small individuals, probably of this species, are com- 

 mon). 



Platyceras carinatum. Hall. (Fig. 195.) (Pal. N. Y.. 

 Vol. V., Pt. II., p. 5, PI. II.) 

 Distinguishing Characters.— Oblique, sub-conical or sub- 

 pyramidal form; minute apex. making 

 one or one and one-half volutions ; 

 rapid expansion below ; strong cari- 

 nation on outside of body-whorl, 

 with commonly a depression on either 

 side; obscure plications; oblique 

 aperture; sinuous peristome; undu- 

 lating concentric striae. 



Found in the Encrinal limestone, 

 and in the Demissa bed, at Section 5 

 ( rather rare ) ; also, rarely, in the middle Trilobite bed. 

 Platyceras thetis. Hall. (Fig. 196.) (Pal. X. Y., Vol. 



Y.. Pt. II., p. 8, PI. III.) 



Distinguishing Characters. —Arcuate 

 outer surface; closely inrolled apex, 

 making one volution; gradually ex- 

 panding lower portion; nearly round 

 aperture; sinuous peristome; lateral 

 tSclSwffii). 1 " longitudinal folds; closely arranged 



lamellose concentric striae. 

 Found in the Demissa bed. at Section 5; and in the middle 

 Pleurodictyum bed, in Avery's Creek. 



Fig. 195. Platyceras cari- 

 inttum (after Hallj. 



