Keyes. J 242 [Oct 19, 
Platyceras latum, sp. nov. (Plate, figs. 10 and 11). 
Shell large, depressed, forming about one and one-half volutions, very 
rapidly expanding from the apex to the aperture, but enlarging trans- 
versely much more than in the opposite direction ; posterior side compar- 
atively very short. Apex small, incurved, but free from the body of the 
shell, and nearly in the same plane as the general curvature. Aperture 
very large, campanulate, transversely elliptic ; lip attenuated and slightly 
sinuous. Surface marked toward the aperture by a few small nearly 
obsolete folds, and by numerous sinuous lines of growth. 
Horizon and locality. Burlington limestone at Burlington, Iowa. 
Platyceras formosum, nov. sp. (Plate, figs. 8 and 9). 
Shell curved, slightly oblique, enlarging rather rapidly to the ample 
irregularly pentalobate aperture, posterior side rather short and concave, 
lateral slopes nearly straight. Apex apparently obtuse, Aperture rather 
large, somewhat pentalobate. Surface marked by five broad well-defined 
longitudinal plications, each of which are composed of several smaller 
folds ; these are crossed by sinuous lines of growth. 
Horizon and locality. Kinderhook beds of Marshall county, Iowa. 
The two specimens of this species found are both attached to the vaults 
of specimens of a Dorycrinus which has been described in the forthcom- 
ing volume of the Illinois Geological Survey now in press. 
EXPLANATION OF PLATE. 
Fig. 1.—Dorsal view of Platycrinus hemisphericus M. and W. with Platy- 
ceras infundibulum M. and W. attached to anal side. 
Fig. 2.—Lateral view of Platycrinus hemispharicus M. and W. with 
Platyceras equilaterum Hall attached to the anal side, partly enclos- 
ing the postero-lateral arms and the stem. 
Fig. 3.—Portion of the vault (viewed obliquely) of Ollacrinus tuberosus 
Lyon and Casseday with Platyceras equilaterum Hall covering the 
anal aperture. 
Fig. 4.—Portion of the vault of Pterotocrinus acutus Wetherby with 
Platyceras chesterense M. and W. attached and covering the anal 
opening. 7, 7, the fractured surfaces of the monstrous alate radial 
dome plates. 
Fig. 5.—Portion of the vault (viewed from above) of Plerotocrinus acutus 
Weth. with Platyceras chesterense attached; another specimen 
showing the five prominent folds in the gasteropod shell. 7, 7, the 
radial dome plates. 
Fig. 6.—Lateral view of Oromyocrinus simplee Trautschold with Platy- 
ceras parasiticum (Trauts.) attached to the anal side. From the 
Subcarboniferous of Russia. 
Fig. '7.—Portion of the vault of Strotocrinus regalis Hall with the Platy- 
ceras removed, showing the anal aperture of the crinoid and the 
concentric impressions made by the lip of the gasteropod shell at 
different periods, which mark the growth of the shell. 
