NAUTILID^i:. 
SILlEIAX species. 
Barrandeoceras Bohemicum, Barrande, sp. 
1838. Lituites Biddulphii, J. de C. Sowerbr, in Murchison’s ^ Silurian 
System/ p. 626, pi. xi. f. 8. 
1851. Xautilus Bohemicus, Barrande, Leonhard & Bronn’s Jahrhuch, 
Heft i. p. 6. 
1867. Xautilus Bohemicus, Barrande, Syst. Sil. de la Bohenie, toI. ii. 
pt. i. p. 146, pi. xxxii., pi. xxxiii., pi. xxxiv. ff. 1, 2, pi. xxxv. f. 1. 
1877. Xautilus Bohemicus, Barrande, ibid, Snpplem. et Serie tardive, 
pi. cccclxxvi. case xi. (young). 
1882 Xautilus Bohemicus, Blake, British Foss. Ceph. pt. i. p. 210, 
pi. xxvii. ff. 1, 2. 
1883. Barrandeoceras Bohemicum, Hyatt, Proc. Boston Soc. Nat. Hist, 
vol. xxii. p. 299. 
Sp. Char. The shell has a flattened discoid form, with not more 
than three volutions, the breadth of which is more than double the 
thickness ; they are all exposed, and there is a central vacuity. 
Each whorl overlaps the preceding one to the extent of about | its 
own breadth. The umbilicus is therefore very wide, but it is 
shallow. The transverse section is elliptical, and is rather deeply 
emarginate on the concave side owing to the overlapping of the 
whorls, just described. The convex border is subtruucate instead 
of being rounded. The ventro-dorsal is to the transverse axis as 
2:1. The body-chamber occupies half the external whorl, and is 
always in contact with the preceding whorl. The aperture, which 
has been observed in a great many specimens in all stages of growth, 
is situated in the plane of the last septum, and its form is similar to 
that of the transverse section. It presents a deep cmargination on 
the periphery. The distance between the septa increases regularly 
but slowly, not exceeding jL the ventro-dorsal diameter. The 
sutures form a wide, shallow sinus upon the sides of the shell, and 
are strongly elevated upon the periphery. The siphunclc is situated 
between the centre and the periphery, but nearer the former than 
the latter. Its elements are cylindrical. The test is ornamented 
merely with lines of growth, which are somewhat stronger in the 
superior third of the sides of the whorls. They form a deep sinus 
upon the periphery, corresponding with that of the aperture. Young 
individuals have, besides the lines of growth, a series of very fine 
longitudinal lines, which do not apparently pass the limits of the 
first wEorl. The cast of the body-chamber is marked with exceed-- 
ingly fine, anastomosing lines (epidermids), representing the surface 
of the mantle of the animal. 
Remarlcs. The species most closely allied to this one are the 
