246 
AUG. F. FOERSTE 
tral than on the dorsal side, especially toward the living chamber, 
and most of all at its aperture, where the difference is strongly 
marked, resulting in the oval outline of the aperture. Faint, 
low, broad vertical ribs mark the cast of the interior of the 
conch ; these number about 5 in a width of 11 mm., near the top 
of the phragmacone. 
The number of camerae in a length equal to the dorso-ventral 
diameter, at the top of the series of camerae counted, is 7, when 
counted along the ventral side of the conch. The sutures of the 
septa are only slightly concave, most of the curvature being ven- 
trad of the center of the conch. At the base of the specimen the 
upward curvature of the sutures is chiefly ventrad of the ventro- 
lateral sides. Toward the top of the phragmacone the upward 
curvature of the sutures begins progressively nearer the middle 
of the lateral sides, and the amount of the upward curvature on 
this ventrad side also becomes greater, the ventral saddles be- 
coming successively higher. The siphuncle is almost in contact 
with the ventral wall of the conch. Its maximum width at the 
bottom of the specimen, within the camerae, is 3 mm., diminish- 
ing to about 1 mm. where it passes through the septa. 
Locality and horizon . — Beloit, Wisconsin; in the buff part of 
the Black River dolomite. 
Specimen No. 998, in the American Museum of Natural His- 
tory. 
Mineral Point syecimen. — In addition to the type of Oncoceras 
pandion, Whitfield figured also a similar specimen (his figure 20) 
from a very fine-grained grayish rock at Mineral Point, Wis- 
consin. Lithologically this rock resembles that enclosing the 
type of Cyrtoceras neleum, from Platteville, Wisconsin. The 
Mineral Point specimen is more compressed laterally, the dorso- 
ventral and lateral diameters at the base of the living chamber 
being 26.5 and 21.5 mm. respectively. Apparently the conch is 
less strongly curved lengthwise, and the sutures of the septa 
curved less strongly upward on the ventral side. The upper- 
most camera is distinctly shorter than those beneath, the speci- 
men being mature. The ventral side of the conch is more nar- 
rowly convex in cross-section than the dorsal side, especially 
toward the living chamber, and most of all near the aperture. 
Janesville specimen. — -In the specimens from Janesville, Wis- 
