NArTILID^. 
61 
and of one millim. near the apex. Septa smooth, with a very slight 
concavity, equal to an arc of about 60°. Sutures straight, and at 
right angles to the spiral axis. 
“ Siphuncle near the ventral side, small in its passage through the 
septa ; having a diameter of six miUim. where the tube has a ventro- 
dorsal diameter of forty-five millim. 
“ The test has a thickness of about one millim. on the outer volu- 
tion. Surface marked by irregular, lamellose, undulating lines of 
growth, which slope in a retral direction, oblique to the spiral axis 
of the tube. The ornamentation consists of strong, transverse, 
prominent, plicate, foliate expansions of the test, inclining towards 
the aperture, and having an elevation of about twenty-seven millim. 
on the outer volution, growing less prominent and more finely 
plicated towards the apex. These expansions are quite regularly 
plicate, and present surface-marking similar to the general surface 
of the tube. The folds or plications are continued along the tube, 
forming rounded, revolving ridges. The sinus in the stria) and 
ornaments of the test is rounded, and has a width equal to twice 
the depth. The internal mould is annulated from the strong trans- 
verse expansions of the test, and shows the furrows and ridges of 
the crenulations, with those of the test. Sutures not impressed. 
“ One specimen, nearly entire, constituting about one volution and 
a half, has a length of 600 millim., with a diameter of 75 millim. 
near the aperture, and measures 210 millim. from the ventral 
margin of the aperture across the volutions. 
“ This species is distinguished by its size, the curvature of the 
tube, the apical angle, and the prominence of the ornamentation. 
The apical portion differs from Gyroceras involve ' [Conrad, sp.] in 
its more rapidly enlarging tube and marked characters of the internal 
mould and surface ornaments. In G. Kerens [Hall, loc. cit. p. 373, 
pi. Ixi. ff. 4-6] the tube is more slender, less involute, and the 
expansions of the test are more frequent and more decidedly 
plicated, but much less elevated. The curvature of the tube in 
G. Matheri [Conrad, sp., Hall, loc. cit. p. 377, pi. Iv. ff. 1-6] is 
distinctive, and the tube is more slender, and with a flattened, 
transverse section. This form \_G. Cyclops'] is a remarkably large 
and well-defined species, and has a horizontal range greater than 
any of the previously described forms, except, perhaps, Cyrtoceras 
cemulum^ [Hall, loc. cit. p. 371].” [Hall.) 
^ Hall, Pal. New York, 1879, vol. v. pt. ii. p. 374, pi. lii. ff. 1-0, pi. lii. a. 
ff. 1-7. See next page. 
- This name must be changed, as it has been used by Barrande for a species 
of Cyrtoceras (Syst. Sil. de la Bohdme, 1867, vol. ii. pt. i. p. 540). 
