eOMPHOCEEATID^E. 
225 
Sj). Char. “ A specimen consisting of the outer chamber and last 
septum, is of moderate size, transversely subcircular, with a very 
slight angularity on the ventral side. Outer chamber rapidly con- 
tracting from near the last septum to the aperture, giving it a 
somewhat conical form, the length being less than the transverse 
diameter of the septum. Aperture trilobed, the ventral opening 
small ; dorsal opening moderately large and subtriangular : the pro- 
portions of the transverse and axial diameters are as three to four. 
Septa moderately deep, with a very regular convexity. Siphuncle 
situated at one third the distance from the ventral margin to the 
centre. Surface marked only by irregular lines of growth.” 
(Hall.) 
Remarks. The specimen which I have doubtfully referred to 6r. 
scrinium is characterized by the remoteness of its septa, and by its 
elliptical form, in both of which features it offers a considerable re- 
semblance to G. ellipticum, M^Coy. The present form may possibly 
be undescribed ; but without better material, it would not be ad- 
visable to found a new species for it. 
Horizon. Niagara Group (Wenlock). 
Locality. Wabash County, Indiana. 
Represented by a single imperfect example. 
b. Endogastric. 
Gomphoceras arcuatum, Sowerby, sp. 
1839. Phragmoceras arcuatum, Sowerby, in Murchison’s Sil. Syst. 
pi. X. f. 1. 
1854. Phragmoceras arcuatum, Morris, Oat. British Foss. 2nd ed. 
p. 312. 
1882. Phragmoceras arcuatum, Blake, British Foss. Ceph. pt. i. p. 204, 
pi. XXV. f. 1, pi. xxvi. ff. 1, 2,2 a. 
1885. Phragmoceras arcuatum (?), F. Roemer, Palseont. Abhandl. 
Band ii. Heft v. p. 127, Taf. x. f. 2. 
Char. Shell curved to an extent equalling half a whorl. 
Section oval, the longer axis in the plane of curvature, the ratio of 
the two diameters being as 11 : 8, when the shell is not compressed. 
The length of the body-chamber equals, if it does not exceed, that 
of its basal diameter. The aperture slopes at an angle of about 45° 
to the plane of the last septum ; its larger orifice is remarkably 
prominent, and uniformly expanded transversely ; the channel con- 
necting it with the smaller orifice is nearly closed for the greater 
part of its length, but gradually opens out as it approaches the 
latter, and forms an elongated oval opening. The smaller orifice, 
