260 
AUG. F. FOERSTE 
49. MONOCYRTOCERAS LENTIDILATATUM SP. NOV. 
PLATE XXXVII, FIG. 1; PLATE XXXVIII, FIG. 1; PLATE XXXIX, 
FIG. 1; PLATE XL, FIGS. lA, B; PLATE XLI, FIGS. 3A, B 
Greenfield specimen . — Specimen consisting of the lower part 
of a living chamber with 11 camerae still attached. A twelfth 
camera is represented by the cast of the interior of one of the 
segments of the siphuncle, at the base of the specimen. Conch 
distinctly curved lengthwise, the radius of curvature of the con- 
vex or ventral side being about 450 mm., and that of the concave 
or dorsal side about the same. The conch is distinctly compressed 
dorso-ventrally. The dorso-ventral diameter at the base of the 
living chamber is 66 mm., the lateral diameter being estimated , 
at 75 mm. The lateral diameter enlarges from 60 mni. at the 
base of the specimen to 75 mm. at the base of the living chamber, 
the intervening distance being 125 mm., measured along the 
ventral side of the conch, but most of this enlargement takes 
place along the lower 5 camerae retained by the specimen. The 
living chamber contracts slightly laterally, in an upward direc- 
tion. The dorso-ventral diameter increases from 53 mm. at the 
base to 60 mm., 5 camerae farther up, and to 66 mm. at the base 
of the living chamber. Apparently it continues to enlarge for 
40 mm. above the suture outlining the base of the living chamber. 
About 6 camerae occur at the top of the phragmacone in a length 
equal to the lateral diameter of the conch, but the uppermost 
two camerae shorten rapidly, indicating that the specimen was 
fully mature. In descending order, the uppermost camera has 
a length of 6 mm., the next beneath of 8 mm., and the next 7 or 8 
camerae of 10 or 11 mm. 
The sutures of the septa curve downward moderately both dor- 
sally and ventrally, and rise laterally to a corresponding degree. 
The concavity of the septum at the base of the specimen equals 
13 mm. When the dorso-ventral diameter is 53 mm., the center 
of the siphuncle is 21 mm., or two-fifths of the dorso-ventral 
diameter, from the ventral wall of the conch. The lateral diam- 
eter of the siphuncle, where in contact with the septum beneath, 
is 13 mm., and it contracts here suddenly to 7 mm. at the be- 
ginning of the septal neck. The lower margin of this neck 
flares out strongly, the length of the neck being slightly over 
1 mm. The sides of the segments of the siphuncle, within the 
walls of the camerae, present straight profiles, the segments hav- 
