NIAGARA FALLS AND VICINITY 211 



Genus platyceras Conrad 



[Ety.: -Xazij^, flat; -/Jfjo.^, horn] 



(1840. An. rep't pal. N. Y. p. 205) 



Shell conic, irregular, with or without the apex inrolled; aperture 

 expanded, often reflexed; peristome entire, often sinuous; surface 

 variously striated^ sometimes bearing spines. 



Platyceras niagarense (Hall) (Fig. 139). 

 Acroculia niagarensis Hall (1852. 

 Pal. N. Y. 2 :288, pi. 60) 



Distinguishing characters. Involute apex, 

 scarcely forming a volution; gradually ex- ^ ; 



panding lower portion, with two or three '- 

 longitudinal folds or undulations; transverse 

 striae, which undulate across the folds and 



., . Fig. 139 Platyceras niagarense 



depressions. 



Found rarely in the lower Rochester shale at Niagara. Also at 

 Lockport (Hall). 



Platyceras angulatum (Hall) (Fig. 140). Acroculia an- 

 g u 1 a t a Hall (1852. Pal. N. Y. 2:289, pi. 60) 



Distinguishing characters. Attenuated apex, form- 

 ing one or two minute volutions; shell below extend- 

 ing in a broad curve, and expanding rapidly toward 

 the aperture, which is much dilated; angulated sur- 

 face, with a sharp carina on the upper and lower outer 

 Fig. 140 Platyceras margins, and an obtuse carina in the middle; trans- 



angulatum 



verse section unequally pentagonal. 

 Found in the lower and middle Rochester shale at Niagara. 

 Rare. Also at Lockport (Hall). 



Genus diaphorostoma Fischer 

 [•Ety.: dtd<popo<^, unlike; rTTo/ia, mouth] 

 (1885. Manual de Conchyliologie; Platyostoma Conrad. 

 1842. Acad. nat. sci. Jour. 8:275) 



Shell with a short depressed spire, a large dilated aperture and 

 with the inner lip lying close against the body whorl. 



