156 
NAUTILOIDEA. 
specimen that measured an inch and a quarter in diameter, whilst 
Billings’s measures only nine lines ; so that the septa would naturally 
he closer together, following the general rule. 
0. explorator is from the Quebec Group of ^Newfoundland. 
With reference to the horizon of the rocks whence the present 
species was obtained, Salter observes {hoc. cit. p. 233) “ The 
great formation which occupies the Arctic lands, or at least skirts 
their icy shores, is a limestone which, from all that can be gathered 
from the fossils, is of Upper Silurian age.” 
Horizon. Silurian. 
Locality, Assistance Bay, Cornwallis Island, Arctic America. 
Bepresented by two small specimens transferred from the Museum 
of Practical Geology. 
Endocerasj sp. 
1855. Orthoceratites duplex, Prado, Sur la geologic d’Alinadeu &c., in 
Bull. Soc. G6ol. de la France, ser. 2, vol. xii. p. 186. 
A very imperfect cast, 14 lines in length and 1 inch in diameter 
at the larger end, with a portion of the siphuucle protruding, does 
not present sufficient characters for specitic determination. The 
septa can scarcely be recognized, and the specimen may be part of 
the body-chamber. It is doubtless the same form as that chronicled 
by M. Casiano de Prado, from Huerta del Llano, in the memoir 
cited above. 
Horizon. Ordovician. 
Locality. Almaden de Azogue (Ciudad- Beal), Spain. 
Transferred from the Museum of Practical Geology. 
Endoceras, sp. 
[Cf. Endoceras multituhulatum h Hall, Pal. of New York, vol. i. p. 59, 
pi. xviii. ff. 2 a, A] 
There is an interesting specimen in the Collection, consisting of a 
fragment (a polished section) of the siphuncle of a slowly tapering 
shell, which appears to be allied to, if not identical with, the Endo- 
ceras multituhulatum, Hall. It differs from this, however, in that 
the sheaths in the cavity of the siphuncle do not extend so far down, 
i. e. they make a more obtuse-angled cone than do those of Hall’s 
^ Hyatt (Proc. Boston Soc. Nat. Hist. vol. xxii., April 1883) has founded the 
genus Vaginoceras upon this species, but so far as it has yet been characterized 
it appears to differ from Endoceras only in having more numerous siphuncular 
sheaths. 
