168 GEOLOGICAL SURVEY OF THE TERRITORIES. 
and continuously rounded from that side all the way around to the con- 
tact with the next volution; aperture therefore nearly circular, its out- 
line being modified only by the slight flattening of the distal side of the 
volutions and their short contact with each other. 
Length, or height, about 55 millimeters; breadth of coil of last volu- 
tion, 70 millimeters ; diameter of aperture, 93 millimeters. 
Position and locality. —Kinderhook division of the Subcarboniferous 
series, Springvale, Humboldt County, Lowa. 
Genus PLATYCERAS Conrad. 
PLATYCERAS TRIBULOSUM (sp. DOV.). 
2 
Plate 41, figs. 6 a and b. 
Shell of medium size, very obliquely and rudely conical, curved but 
not coiled; apex free, slender, pointed, incurved, and turned a little to 
the left side; body expanded; aperture very irregular in marginal out- 
line, expanded i in front, narrower behind, and having a prominent double 
lobe beneath the umbonal portion of the shell. Surface marked by the 
ordinary lines of growth, and also by, three longitudinal rows of hollow 
spines arranged upon the dorsal aspect of the shell, the rows extending 
back more than half the length of the shell and containing five or six 
spines each. 
Length of the shell from beak to front margin, 28 millimeters; ; breadth 
of its aperture, 21 millimeters. 
This species is especially characterized by its spines, arranged in three 
rows, and the irregular character of its margin. It differs too much 
from any described | species to need detailed comparison, but it may be 
compared with the two spinous species, P. biserialis Hall, from the same 
formation, and P. dumosum Conrad, from the Devonian rocks of New 
York. 
Position and locality —Burlington limestone division of the Subearbon- 
iferous series, Burlington, Iowa, where it was obtained by Mr. Charles 
Wachsmuth. 
Genus NATICOPSIS McCoy. 
NATICOPSIS MONILIFERA (sp. NOv.). 
Plate 42, figs. 3a, b, and ¢. 
Shell small, subglobose; spire short, obtuse, and its immediate apex 
flattened; volutions about six, but the apical ones are very small, the 
last one constituting the greater part of the shell, broadest upon its 
basal or proximal portion, the proximal side of w hich is somewhat ab- 
ruptly rounded inward to the aperture; the small volutions of the apex 
are plain, but upon the distal border of. the two last ones, adjacent to the 
suture, there is a conspicuous row of small nodes, constituting a pretty 
ornamentation of the shell; the remainder of the surface is smooth 
and has a polished aspect, upon which a good lens reveals fine striz of 
growth ; aperture suboval in outline ; inner lip having a distinet callus, 
especially i in front; outer lip thin, its border sinuate, having an almost 
distinet notch just in front of the row of nodes. 
Extreme length, 10 millimeters; extreme diameter of the last volution 
nearly the same. 
Position and locality— Upper Coal Measures, Pleasant Hill, Cass 
County Mo., where it was obtained by Prof. G. C. Broadhead. 
