20 
NATTTILOIDEA. 
Trochoceras tortuosum ?, J. de C. Sowerby. 
1839. Lituites tortuoms, J. de C. Sowerby, in Murchison’s Sil. Syst. 
pt. ii. p. 622, pi. xi. f. 3. 
1867. Trochoceras oxynotum, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p. 91, pi. xiv. IF. 1-11. 
1882. Trochoceras tortuosum, Blake, British Foss. Ceph. pt. i. p. 221, 
pi. xxi. £E. 3, 3 a. 
Sj). Char. Shell increasing its diameter about twice for each 
volution. ^‘The outer whorls slightly overlap the inner, and 
scarcely any elevation is observable. The section is rounded- 
lanceolate, rising to the greatest thickness at ^ the whorl-breadth 
from the umbilical edge, whence there is a gentle slope to the front, 
which is subangular. Ratio of thickness to breadth as 13 to 18. 
No ornaments. The shell is of considerable thickness. The septa 
bend slightly backwards on the inner side of the whorl, and then 
rapidly forwards, meeting at an angle on the front. They are very 
numerous, 50 per whorl; the septal surface has a convexity of | 
the long diameter of the whorl, the inner part being flatter. The 
siphuncle is external in the angle at the front, and has a diameter 
on the septal surface of ^ the whorl-diameter. Diameter about 
30 lines.” {Blake.) 
Remarks. Sowerby’s type is in the collection of the Geological 
Society. It is stated by Professor Blake to consist of two pieces, 
of which the larger one only was flgured ; when put together the 
two “ form an ordinary involute TrockocerasT 
There seems good reason for supposing that the present species is 
identical with Barrande’s, the very remarkable form of the whorl 
suggesting this connection ; the two forms agree also in other par- 
ticulars, such as septal characters, position of siphuncle, &c. A 
large specimen in the British Museum, though somewhat crushed, 
compares very well with Barrande’s flgure of T. oxynotum (pi. xiv. 
fF. 9-11) in the closeness of the septa, and the numbers and pro- 
portions of the whorls. 
Horizon. Wenlock Shales. 
Localities. British : Dudley, Worcestershire ; ? Garcoed, Usk, Mon- 
mouthshire. — Foreign : Xosorz, Bohemia. 
Represented in the Collection by four specimens, about one of 
which there is no information ; it is in all probability from the 
Lower Ludlow of the West of England. Another of the British 
examples (No. C. 2018) was presented by J. E. Lee, Esq., E.G.S. 
