242 
AUG. F. FOERSTE 
36. MAELONOCERAS HYATT 
Genotype: Phragmoceras praematurum Billings 
Laterally compressed cyrtoceracones, with the ventral side 
more narrowly rounded than the dorsal. The living chambers 
are short, and their apertures, in the typical specimens, are con- 
tracted and pear-shaped. The sutures of the septa curve slightly 
downward laterally. The siphuncle is near the ventral side, and 
its segments are narrowly fusiform. 
Cyrtoceras metellus Billings from the Canadian of Point Levis, 
in the province of Quebec, Cyrtoceras falx Billings from the 
Black River of Pauquette Rapids, in Ontario, and Cyrtoceras 
arctioameratum Hall from the Guelph of Ontaria are not con- 
generic with Maelonoceras praematurum. Possibly the form 
figured by Whitfield under Cyrtoceras camurum (Geol. Wis- 
consin, 4, 1882, p. 231, pi. 7, figs. 7-9) is a true Maelonoceras. 
37. MAELONOCERAS PRAEMATURUM (BILLINGS) 
PLATE XXXIX, FIGS. 6 A, B, C; PLATE XLI, FIG. 7 
Phragmoceras praematurum Billings; Canadian Naturalist, vol. 5, 
1860, p. 163, figs. 20 
Maelonoceras praematurum Hyatt; Proc. Boston Soc. Nat. Hist., 
vol. 22, 1884, p. 280 
Two specimens belong to the set described by Billings under 
the name Phragmoceras praematurum, and both were figured. 
The specimen represented by figure 20, accompanying the orig- 
inal description, shows most of the details included in this de- 
scription, and hence is here regarded as the type. 
Type. — Conch strongly compressed laterally, and strongly 
curved length-wise, the siphuncle being close to the ventral side. 
The conch attains its greatest dimensions 5 mm. above the base 
of the living chamber. Here its lateral diameter is 16 mm. and 
its dorso-ventral one is 18.5 mm. The conch is more narrowly 
rounded on its ventral side, the radius of transverse curvature 
here being 5 or 6 mm., while that of the dorsal side is 8 mm. The 
convex lengthwise curvature of the ventral side has a radius of 
25 mm., and that of the concave curvature of the dorsal side is 
about the same, at least within the limits of the type specimen. 
The latter consists of the living chamber with 5 complete cam- 
erae attached. In addition, parts of 2 camerae prolong the dorsal 
outline of the specimen. The upper half of the living chamber 
narrows toward the aperture, where the lateral diameter is 
