176 
PALAEONTOLOGY OF NEW-YORK. 
Fig. 8 a, b. Views of the aperture and of the spire of a large individual, where the last 
volution is free, and the peristome continuous and somewhat expanded on the 
left side. 
Fig. 9 a, b. The aperture and lower side of a large specimen, where the volutions are con¬ 
tiguous, the umbilicus is very small, and the peristome continuous ; the outline 
slightly sinuate just below the body volution, and expanded upon that side. 
Geological position and locality . In the Oriskany sandstone : Cumberland, Md. 
Platyceras magnificum (n.s ). 
Plate CXIX. Fig. 1-6. 
Shell obliquely subovate. Spire depressed below the plane of the outer 
volution : volutions two or three, very rapidly expanding and becoming 
extremely ventricose below, usually free or with the first one contiguous; 
aperture expanded, subcircular, campanulate, and often with the margin 
reflexed, particularly on the left side. 
Surface marked by distinct transverse lamellose undulating striae. 
This species has some resemblance to P. ventricosum , but differs in its more ra¬ 
pidly attenuating spire and the freedom of the volutions, as well as the comparative¬ 
ly greater expansion of the aperture. In some of the specimens the surface shows 
undulations in the striae, indicating the former existence of sinuosities in the margin 
of the shell; but such features are rarely seen, or scarcely visible in the peristome 
of the specimens examined. 
Fig. 1 a, b. View of the spire and aperture of a young shell. ( The volutions are actually 
free to the apex, although not distinctly represented in the figure.) 
Fig. 2 a, b. A larger specimen with free volutions, having the aperture abruptly expanded. 
Fig. 4 a, b. A larger specimen, with the volutions free and the peristome less expanded. 
Fig. 5 a, b. A larger specimen, having the apex broken off. This specimen presents a sinuo¬ 
sity in the posterior side of the aperture. 
Fig. 6 a, b. View of the aperture and spire of a large specimen in which all the parts are 
symmetrical and well preserved, and the volutions are free except at the extreme 
apex. This figure is represented as of the natural size ; the extreme length being 
three inches and three-fourths, while the aperture is two inches and three-eighths 
in height, and a little more than two inches and a half in length. 
Geological position and locality. In the Oriskany sandstone : Cumberland, Md. 
