AMERICAN PALEOZOIC CEPHALOPODS 
253 
at the top of the phragmacone it is 15.5 mm., indicating a mod- 
erate lateral compression of the conch. There is a slight ten- 
dency toward angularity in the cross-section of the conch, along 
the median line of its ventral side, especially toward the top of 
the phragmacone. 
Counting along the ventral side of the conch, there are 7 cam- 
erae in a length equal to the dorso-ventral diameter of the conch 
at the top of the series of camerae being counted. The sutures 
of the septa are directly transverse on the dorsal and dorso- 
lateral sides of the conch, but they curve upward on approach- 
ing the ventral side of the conch, producing low ventral saddles. 
The siphuncle is close to the ventral wall of the conch. At 
the base of the specimen, the diameter of the siphuncle, where it 
passes through the septum, is slightly over 1 mm. Very faint 
vertical ribs, easily escaping attention, mark the cast of the 
interior of the phragmacone. 
Locality and horizon . — Described from the “Buff limestone of 
the Trenton limestone group referred by Bassler, in his Biblio- 
graphic Index, to the Platteville member of the Black River. 
The type specimen is labelled as coming from Beloit, Wisconsin. 
Holotype. — No. 999, American Museum of Natural History, in 
New York City. 
Remarks. — The appearance of greater height in the camerae is 
due chiefly to the small curvature of the conch lengthwise, owing 
to which the septa are less closely crowded together on the dorsal 
side of the conch, measuring only 5.5 camerae in a length 
of 10 mm., instead of 8 camerae as in the smaller specimen of 
Oncoceras plebeium figured by Whitfield. 
43. WESTENOCERAS GEN. NOV. 
Genotype: Cyrtoceras manitabense Whiteaves. Trans. Royal Soc. 
Canada, vol. 7, sec. 4, 1890, p. 80, pi. 13, figs. 3-5; pi. 15, fig. 4 
Conch slender, sub-fusiform, nearly straight along the dorsal 
side, except at the aperture, but distinctly curved along the 
ventral side. Aperture oblique, inclining downward from the 
ventral toward the dorsal side. Sutures of the septa curving 
strongly downward laterally, but rising dorsally and ventrally 
into distinct saddles, which rise higher on the ventral than on 
the dorsal side. Siphuncle nearer the ventral than the dorsal 
side, described as “nearly cylindrical, but very slightly expanded 
between the septa and as slightly contracted where it intersects 
