378 
PALEONTOLOGY OF NEW YORE. 
three of them varies from thirty to forty mm. Sinus abrupt, angular, having 
a depth of about four mm. on the outer volution, and very marked in the 
raised expansions. 
Internal mould marked by regular, prominent annulations, corresponding 
in frequency to the external ornaments, and showing the longitudinal ridges 
and furrows of the crenulations. 
The diameter across the disc, in a large specimen, measures 125 mm., and 
the tube has a diameter of thirty-three mm. at the aperture. 
This species is distinguished from G. laciniosum by its nearly circular trans¬ 
verse section, and more elevated and less regularly plicated transverse expan¬ 
sions of the test. The annulations of the internal mould are much more 
prominent and distant than in G. trivolve, and the transverse section is different. 
In G. undulatum and G. paucinodum the shell is characterized by several closely 
coiled volutions. The specimens referred to this species show slight, but unim¬ 
portant variations in the transverse section of the tube and the number of volu¬ 
tions. This latter variation is principally due to the tendency of the outer 
volution to become straight. 
Formation and localities. In the Upper Helderberg limestone, at Schoharie 
and Catskill, N. Y. 
Gyroceras undulatum. 
PLATES LIII, EIG. 1-6; LIV, PIG. 5. 
Cyrtoceras undulatum, Vanuxem. Geolog. Surv. of N. Y. : Rep. Third Dist., pp. 139, 140, fig. 2. 1842. 
Gyroceras undulatum (Vandx.), Hall. Descriptions of New Species of Fossils, etc., p. 38. 1861. 
“ “ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 66. 1862. 
“ “ “ “ Illustrations of Devonian Fossils: Cephalopoda, plate 56, 
tigs. 1, 2. 1876. 
Shell discoid, closely coiled, making from two to three volutions, which are 
not contiguous. Transverse section broad, subangular transversely ovate; 
lateral diameter the longer. The tube is somewhat flattened on the ventrum, 
and angular at the ventro-lateral sides and on the dorsum; regularly and 
gradually enlarging. Apical angle about 7°. 
