1889.] 
279 
[Foerste. 
end 20 mm., the specimen being 50 mm. long. No septa are shown 
on this specimen. What seems to be the surface of this specimen 
is smooth. 
Orthoceras (eu-orthoceras?) ignotum, sp. nov. 
(PLATE VII, FIG. 4.) 
Several specimens of this species have been found at Hanover, 
Indiana. The type specimen is 34.5 mm. long and contains in that 
length eleven chambers and twelve septa. The septa are 3.2 mm. 
apart, where the diameter of the shell is 11.2 mm. The specimen 
has a diameter of 14 mm. at the larger end. In a specimen 19 mm. 
long, 12.5 mm. broad at the larger end, and 11 mm. at the smaller 
extremity, there are six chambers and seven septa. The septa are of 
medium convexity, forming an arc of about 100°. The siphon is 
almost central, and has a diameter of about 1.8 mm. where the diam- 
eter of the shell is 11.5 mm. The greatest diameter of the siphon 
seems to be near the upper part of each chamber, each annulated 
portion tapering rapidly towards the upper septum, and slowly tow- 
ards the lower septum, the connecting aperture having a diameter of 
1.3 mm. The character of the surface could not be satisfactorily de- 
termined but seems to have been smooth. This species may belong 
to the larger subgenus Geisonoceras. 
If fig. 2 c, PI. 29, Pal. N. Y., Vol. n, does not belong to 0. vir- 
gulatum , then scarcely any Clinton form could more appropriately 
be identified with that species than the Indiana form. 
Orthoceras (eu-orthoceras?) rhythmoides, sp. nov. 
(plate VIII, FIG. 2.) 
A single fragment was found at Brown’s Quarry, near New Car- 
lisle, Ohio. In a length of 29.2 mm., there are ten chambers and 
eleven septa. The specimen has a diameter of 28 mm. at the smaller 
extremity and shows no appreciable increase in size in a distance 
of 30 mm. What seems to be a portion of the siphon was almost 
central in position. As nearly as could be determined from the small 
portion of a septum shown, the convexity of the septa does not ex- 
ceed 96°. Perhaps this form belongs to the larger subgenus, Gei- 
sonoceras. 
It is readily distinguished from Orthoceras clavatum, Hall, from 
the Clinton Group of New York, by means of its much smaller 
apical angle, the sides in the Ohio form, in the short distance pre- 
served, being almost parallel. 
