CEPHALOPODA. 
35 
Chamber of habitation shorter than the transverse diameter. Grand aper¬ 
ture large, oval, with a marked sinus on the ventral side, forming a small 
aperture. Crenulated zone narrow, marked by fine elevated transverse lines 
or nodes. 
Air-chambers shallow, having a depth of 2.5 mm. near the outer chamber. 
Sutures straight, with the exception of a slight retral bend on the ventral 
side adjacent to the siphuncle. 
Siphuncle small, ventral, situated close to the walls of the air-chambers. 
Surface marked by irregular lamellose lines of growth which become aggre¬ 
gated into fascicles near the aperture. 
Internal mould smooth. 
A fragment preserving the chamber of habitation and four attached air- 
chambers has a length of 30 mm., and a greatest diameter of 28 mm. 
Distribution. In the arenaceous shales of the Chemung group, at Belmont 
and Belvidere, Alleghany county. 
Gomphoceras potens. 
PLATE CXXII, FIG. 8. 
Gomphoceras potens, Hall. Pal. N. Y., vol. v, pt. 2, p. 351. 1879. 
CYRTOCERAS, Goldfuss. 1832. 
Crytoceras subcompressum. 
PLATE CXXIX, FIGS. 2, 3. 
Cyrtoc&ras subcompressum. Hall. Fifth Ann. Kept. State Geologist. Expl. pi. (129) 14, figs. 2, 3. 1886. 
Shell large, robust, exogastric, curved, a mature individual making a quadrant 
of a circle. Transverse section broadly oval. Tube regularly enlarging from 
the apex to the aperture. 
Chamber of habitation large. Air-chambers regular, about 7 mm. in depth. 
Siphuncle nearly one-fourth the diameter of the tube, excentric, nummu- 
loid, abruptly contracted at its passage through the septa. 
