OETHOCEEVTID^. 
9 
The cross-section of the shell is elliptical. The length of the body- 
chamber is about 5 that of the entire shell. The difference between 
the septa varies considerably in different specimens, being from ^ 
to 3 the diameter, roughly speaking. The convexity of the septa is 
equivalent to about ^ the diameter. The siphuncle is small, cylin- 
drical, and measures about -jij the diameter of the shell. 
Remarhs. The matrix in which this species occurs is a sandstone, 
and the shell is always completely dissolved away, so that the spe- 
cimens consist of casts in sandstone. The species has been found 
in a like condition in the sandstones of 3day, in Normandy, whence 
it was obtained by M. Eudes Deslongchamps, and submitted by him 
to M. Barrande, who recognized it as identical with his species from 
Mt. Drabow, in Bohemia. 
Horizon. Stage D, bande cl2 ( = Llanvirn Series ?). 
Locality. Mt. Drabow, Bohemia. 
Fairly well represented. 
Orthoceras decrescens, Billings. 
1857. Orthoceras decresceris, Billings, Geol. Surv. of Canada, Rep. of 
Progress for the years 185.3-56, p. 337. 
1863. Orthoceras decrescens, Bill. Geol. of Canada, App. p. 950. 
I 860. Orthoceras decrescens, Safford, Geol. of Tennessee, p. 289. 
^p. Char. “ Shell annulated, with subacutely rounded and 
slightly undulating ridges, which arc two lines distant at a dia- 
meter of fourteen lines, somewhat more approximate towards the 
apex ; intervening spaces regidarly concave and half a line in depth. 
Section circular, tapering at the rate of two lines to the inch ; 
siphuncle small, eccentric, about one sixth of the diameter from 
the centre ; septa concave, slightly oblique, their ventral margins 
nearest the aperture, distant two lines at a diameter of eleven 
lines. Differs from all other described annulated species of the 
Silurian [Ordovician] limestone of America in its more rapid rate 
of tapering.” 
I have given Billings’s description in full, because it includes 
some specific features which are not observable in the British- 
Museum example. 
I may add that the surface of the test is covered with fine trans- 
verse striae. 
Horizon. Black River ( = Llandeilo Limestones ?). 
Locality. St. Joseph Island, Lake Hurou, Chnada. 
Represented by one example. 
