62 
NAUTILOIDEA. 
RemarJrs. A fairly good specimen of the present species is con- 
tained in the British Museum Collection. It is a cast with some 
fragments of the test adhering to it. 
Horizon. Upper Helderberg. 
Locality. Columbus, Ohio. 
Kepresented in the Collection by a single example. 
Gyroceras trivolve, Conrad, sp. 
1840. Cyrtoceras trivolvis, Conrad, Geol. Surv. New York ; Pal. Dept., 
Third Ann. Ilep. p. 206. 
1861. Gyroceras trivolvis (Conrad), Hall, Descriptions of New Species 
of Fossils, &c. p, 37. 
1862. Gyroceras trivolvis (Conrad), Hall, Fifteenth Reg. Rep. New 
York State Cab. Nat. Hist. p. 65. 
1876. Gyroceras trivolvis (Conrad), Hall, Illustrations of Devonian 
Fossils, Cephalopoda, pi. liv. ff. 1-5, and pi. Ivi. f. 4. 
1879. Gyroceras trivolve, Hall, Nat. Hist. New York, Palaeont. vol. v. 
pt. ii. p. 374, pi. lii., pi. Hi. a. ff. 1-7. 
Sp. Char. “ Shell involute, subdiscoidal, openly coiled. Spiral 
rapidly enlarging, making from one and a half to two volutions. 
The last half of the outer volution in large individuals shows a 
tendency to become straight, and tangent to the spiral. Transverse 
section subcircular. Tube regularly and gradually enlarging from 
the apex. Apical angle about 9°. 
“ The chamber of habitation has a length equal to once and a 
half the diameter of the tube at the last septum. Crenulations pre- 
served on the internal mould, as low, rounded, longitudinal ridges, 
with fine intermediate stria;. Aperture straight and horizontal, 
entire, with a distinct sinus in the ventral margin. 
Air-chambers regular, numerous, having a depth of 4-5 millira. 
Septa smooth, thin, with a concavity greater than the depth of one 
air-chamber, or equal to an arc of 110°. Sutures straight, and at 
right angles to the spiral axis. 
“ Siphuncle near the ventral side, not expanding in the cavities 
of the air-chambers. 
“ The test has a thickness of *75 millim. Surface marked by 
very fine, undulating, lamellose lines of growth, crossed by revolving 
striae and obscure furrows. Tube ornamented with numerous trans- 
verse, plicate folds, or expansions of the test, having an elevation of 
about two miUim. on the outer volution, and usually corresponding 
in frequency with the septa. Sinus distinct, having a width of 
more than twice the depth. 
