ORTHOCERATID^. 39' 
Sj). Char. Shell slightly curved. Section elliptical, the ratio 
of the two diameters being as -11 : 38. The rate of increase is^ 
about 1 in 12. The dimensions of the fragment are the follow- 
ing : — Total length about 8 inches, of w^hich ^ is taken up by the 
body-chamber. The greatest diameter of the latter is 41 lines ; of 
the septate part of the shell 35 lines. The length of the body- 
chamber cannot be precisely determined, but the part preserved 
exceeds the basal diameter by about ; it decreases slightly in 
diameter towards the aperture, where there may have been a con- 
striction. The septa are somewhat undulating and distant about ^ 
the longer diameter, with a convexity of nearly 4 that diameter. 
The siphuncle is large and cylindrical, with little or no inflation 
between the septa; its diameter is 7 lines, or ^ that of the longer 
diameter of the shell. It is eccentric in position, and is situated 
about f across the longer diameter, measuring from its centre to 
the margin of the shell. The surface is ornamented with very 
strong transverse striae, having an upward imbrication, and these 
are crossed longitudinally, apparently at rare intervals, by faint 
ridges, which appear also upon the cast. The striae (fig. 3, c) are 
generally from 2 to 24 lines distant from each other, but occasionally 
the interval separating them is not more than li line ; they are 
distinctly marked upon the cast of the body-chamber (fig. 3, «), 
which is also covered with fine, wavy, irregular, impressed lines 
(fig. 3, d\ produced probably by the mantle of the animal. These 
markings are observable in many other genera of fossil Cephalopods, 
such as Cyrtoceras, Trochoceras, Goniatites, &c. 
Remarks. This fine shell was at first taken for a Cyrtoceras^ on 
account of its curvature, but the position of the siphuncle, lower 
rate of tapering, and distance of the septa, distinguish it completely 
from that genus. 
With reference to the horizon of the rocks whence this species 
was obtained, the following remarks in Wr. Etheridge’s paper are 
worthy of note : — “ .... few as are the Lower Silurian fossils 
brought home, they are enough to show the succession to be much 
the same as in British North America and the British Islands ; and 
the Upper Silurian [Silurian] fossils of Dobbin Bay, Cape Hilgard, 
Cape Louis Napoleon, Offley Islands, &c., confirm this unmistak- 
ably. Moreover, we are enabled to correlate these Upper Silurian 
fossils with the Wenlock group of Britain ; but, nevertheless, they 
have a facies allying them to the American types rather than to our 
own.” 
I regret that the space at my command has not permitted me to 
