264 
AUG. F. FOERSTE 
aperture is 39 mm.; its dorso- ventral diameter may be slightly 
greater. Its general form is circular, but along its ventral mar- 
gin it is distinctly angular, though the angularity still is rounded. 
The margin of the aperture curves more or less horizontally in- 
ward for a distance of 3 or 4 mm. ; perhaps less toward the ven- 
tral angularity. At this angularity the margin of the aperture 
curves downward, forming the hyponomic sinus. 
In a second specimen, (Plate XXVI, Figs. lA, B) from the 
same locality and horizon, the specimen is more compressed lat- 
erally, probably by pressure during fossilization. The length- 
wise ventral outline is more convex. The aperture is well ex- 
posed, including the hyponomic sinus, but it also is compressed 
laterally. 
The surface of casts of the interior of the conch usually is 
faintly ribbed vertically along the phragmacone. The surface of 
the shell is crossed transversely by low broad lines of elevation 
of variable strength, representing successive stages of growth. 
These serve to locate the ventral side of the conch, where they 
curve distinctly downward. 
At the base of the eighth camera below the living chamber of 
one specimen, where in the present flattened condition of the 
specimen the diameters at right angles to each other are 42 and 
37 mm., the maximum diameter of the siphuncle is 8.5 mm. and 
its passage through the septum is 5.5 mm. in diameter. At its 
contact with the overlying septum, the exposed segment of the 
siphuncle is in contact with the latter over its entire width, 
forming a circular area of contact, which is penetrated by the 
passage of the siphuncle through the septum in a strongly excen- 
tric position, its ventral margin being less than 1 mm. from the 
ventral margin of the segment. The ventral side of the segment 
is curved obliquely, in a direction approximately parallel to the 
ventral wall of the conch. 
Locality and horizon . — Little Four Mile creek, near Oxford, 
Ohio ; in the lower part of the Whitewater member of the Rich- 
mond formation. In the collection of Prof. W. H. Shideler, at 
Miami University. 
Faber specimen . — A vertical section, in a dorso-yentral direc- 
tion, through a specimen (Plate XXVI, Figs. 2 A, B) collected 
by Mr. C. L. Faber at the same horizon on Little Four Mile 
creek, exposes the siphuncle sufficiently to indicate its relative 
