362 PALEOZOIC PALEONTOLOGY. 
The dimensions of a very large individual are: maximum diameter, 
85 mm.; maximum height, 55 mm. Those of a smaller specimen 
are: maximum diameter, 28 mm.; maximum height, 25 mm. 
Remarks.—As it usually occurs in the Oriskany fauna of New 
Jersey, this species does not attain the great size of the specimen 
whose dimensions are given above, the average size being from 30 
mm. to 40 mm. in diameter. ‘The species is exceedingly variable, 
and all of the specimens of this general type so far recognized in the 
Oriskany of New Jersey seem to be included within the limits of this 
species as recognized by Hall. 
PLATYOSTOMA DESMATUM (Clarke). 
Plate XLIX., Fig. 12. 
1900. Diaphorostoma desmatum Clarke, Mem. N. Y. St. Mus., No. 
swol, LLL. p. 29: pl.73, ties. lg— 19: 
This species agrees in all respects, except size and surface markings, 
with P. ventricosa. It does not grow so large as that species, the 
largest individual observed being 25 mm. in diameter and 18 mm. 
high. The surface markings differ from P. ventricosa in having, in 
addition to the transverse lines of growth, which are finer and more 
regular, other fine revolving lines most prominent in the interspaces 
between the transverse lines, which give to the surface of the shell a 
cancellated appearance. 
PLATYCERAS TORTUOSUM Hall. 
Plate XLIX., Figs. 18-14. 
1859. Platyceras tortuosum Hall, Pal. N. Y., vol. IIL, p. 472, pl. 
113, figs. 1-5. 
Description.—Shell erect, spirally subconical in form, making about 
one volution, which increases gradually in size towards the scarcely- 
expanded aperture. One side marked by a spiral sinus, which extends 
from the apex to the margin of the aperture. 
