]\Iarylaxd Geological Survey 473 



This species in the character of the undulations, bears some resemblance 

 to P. platysiomum of the Lower Helderberg of New York ; but its shape 

 and the constriction of the aperture show it to be distinct from other 

 species of the genus. 



Diameter of shell 4.5 cm. to 8 cm. ; of aperture 3.2 cm. to 6 cm. 



Occurrence. — Oriskany Formation, Eidgely Member. Hancock. 



CoUection. — Maryland Geological Survey. 



[Ohern.] 



Platyceras patulum Hall 



Plate LXXXIII, Fig. 4 



Platyceras patulum Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 477, pi. cxix, 

 fig. 3, 1861. 



Description. — " Shell subhemispheric. Spire forming about three volu- 

 tions, which are usually contiguous, sometimes free, very rapidly expand- 

 ing, the last one extremely ventricose and assuming a hemispheric form ; 

 apex much below the plane of the last volution. Aperture nearly circular ; 

 peristome much expanded upon the side of the body volution, and thicken- 

 ing below in the form of a columellar lip. Siarface transversely striated." 

 Hall, 1859. 



Occurrence. — Oriskaky Formation, Ridgely Member. Cumberland. 



Collection.— Yr&-nk Hartley. 



[Ohcrn.] 



Platyceras reflexum Hall 



Plate LXXXIII, Figs. 5, 6 ; Plate LXXXIV, Figs. 1, 2 



Platyceras reflexum Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 477, pi. cxx, 

 figs. 1-7, 1861. 



Description. — " Shell spiral, obliquely or arcuately subconical, spirally 

 ascending; the apex consisting of one or two free, but closely approxi- 

 mating volutions ; the body volution diverging, and spreading somewhat 

 rapidly towards the aperture : aperture broad, the peristome often sinuous 

 and sometimes abruptly expanded: volutions round or subangular, and 

 rarely distinctly angular, with the aperture subquadrate. Surface trans- 

 versely striate ; the strife sometimes bent abruptly backwards on the sur- 



