272 



Fig. 194. Platyceras 

 erectum (after Hallj. 



Platyceras ERECTUM. Hall. (Fig. 1U4.) (Pal.N.Y.,Vol. 

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



Distin^-uishing Characters.— Closely iiirolled apex, for one 

 and one-half volutions; rapidly exj)anding 

 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.— 0\)]i(\\m, 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 commonh^a depression on either 

 side ; obscui-e 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. N. Y., Vol. 

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



Distinguisliing Cliaracters. — Arcuate 

 outer surface; closely inrolled apex, 

 making one volution ; gradually ex- 

 panding lower poi'tion ; nearly round 

 aperture; sinuous peristome; lateral 

 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. ]".i5. Platyceras cari 

 natum (after Hall). 



Fig. 196. Platyceras 

 thetis (after Hall). 



