236 
AUG. F. FOERSTE 
part of the lateral margins of the aperture, measured along the 
median part of the lateral sides, about 108 mm. Depth of 
hyponomic sinus below level of highest part of lateral margins 
of aperture, 36 mm. 
At the base of the hyponomic sinus the lateral diameter of the 
living chamber is 93 mm. ; 100 mm. farther down, measured 
along the ventral side of the conch, this diameter is 83 mm.; 
100 mm. still farther down it is 67 mm. ; indicating a rate of 
diminution of 10 and 16 mm. respectively in the distances men- 
tioned. Estimating the remainder of the length of the last volu- 
tion, in an apicad direction, as 120 mm., the lateral diameter of 
the conch at the beginning of its last volution, was at least as 
small as 47 mm., but probably was smaller, since the< rate of 
diminution of the lateral diameter of the conch appears to have 
been greater in an apicad direction. In fact, in some specimens, 
which show parts farther apicad, the rate of diminution of parts 
narrower than 47 mm. equals 25, and occasionally even 28 mm. 
in a length of 100 mm. The apical end of the conch has not been 
discovered, but it is estimated that the large conch here described 
included at least 2 complete volutions and possibly more or less 
of a third volution. The umbilicus may have been penetrated by 
a perforation about 10 mm. in diameter, but this part is not 
well preserved in any specimen. 
The conch is depressed dorso-ventrally, the general outline of a 
cross-section of the larger volution being transversely elliptical, 
with the dorsal side distinctly and broadly impressed. The ratio 
of the dorso-ventral to the lateral diameter varies from 67 % to 
70% in different specimens. The ventral side is less strongly 
curved than the dorsal, the maximum curvature of the lateral 
sides being slightly nearer the ventral side of the whorl. In 
general, the lateral sides of the whorl converge toward the 
dorsal side. In one specimen, with a width of 66 mm. at the 
base of the living chamber, the width of the impressed zone at 
this point was 25 mm., its depth being 4 mm. In its original 
condition the conch was symmetrical, but, in the fossil state, 
one of the lateral sides often is flattened slightly or more dis- 
tinctly; usually on that side of the specimen which, in the 
original position of the fossil in the rock, faced downward. In 
those specimens in which one of the lateral sides is flattened, the • 
opposite side usually shows the normal transverse convexity. 
