GASTEROPODA.  5 



Platyceras erectum. 



PLATE II, FIGS. 4-11. 



Acroculia erecta Hall. Geology of N. Y. Surv. Fourth Geolog. Dist., pp. 172, 174, f. 6. 1843. 

 Platyceras erectum Hall. Descriptions of New Species of Fossils, etc., p. 4. 1861. 

 " " Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 32. 1862. 



" " " Illustrations of Devonian Fossils: Gasteropoda, pi. 2. 1876. 



This species, originally described in the Corniferous limestone, occurs also in 

 the Hamilton group. The spire at the apex is closely enrolled for about one 

 volution and a half, beyond which the body-volution becomes somewhat 

 rapidly expanded, with the aperture often spreading. The specimens are often 

 more arcuate than the figure in the Geological Report, and the aperture 

 oblique, with the peristome sinuate. 



The surface is marked by closely arranged revolving lamellose striae, which, 

 upon the lower half of the body-volution, are abruptly arched along narrow 

 bands, corresponding with former sinuosities of the aperture. 



Formations and localities. In the limestone of the Upper Helderberg group, 

 Williamsville, and near Buffalo; and in the Hamilton group at York, Moscow, 

 Darien, and other places. 



Platyceras carinatum. 



PLATE II, FIGS. 1-2-29. 



Platyceras carinatum Hall. Descriptions of New Species of Fossils, etc., p. 5. 1861. 

 " Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 33. 1862. 

 " " " Illustra' ions of Devonian Fossils: Gasteropoda, pi. 2. 1876. 



Shell obliquely subcorneal or subpyramidal ; the nucleus or apex minute, and 

 making from one to one and a half volutions which are vertically com- 

 pressed, and below which the body- volution is abruptly expanded ; the 

 dorsum angular, or marked by an angular carina, which often becomes 

 double in old shells, or* is rounded on the summit. This angularity or 

 earina indicates, by the direction of the striae, the existence of a sinus in 

 the peristome from an early period of growth; and sometimes there may 

 have been two such sinuosities close together, giving the double carina. 

 There is usually a depression along one or both sides of the carina, with 



