266 
AUG. F. FOERSTE 
to Diestoceras, the side along which the septa are more approxi- 
mate is regarded as ventral, while that along which they are 
more distant from each other is regarded as dorsal. Along the 
ventral side of the specimen 7 camerae occupy a length of 
36 mm., while along the dorsal side the same 7 camerae occupy 
a length of 46 mm. The sutures of the septa rise slightly from 
the ventral toward the dorsal side of the conch. They are ap- 
proximately straight. The septa may have been more deeply 
concave than in Diestoceras indianense, but the exposed septum 
at the base of the specimen may have secured its present form 
from crushing. No trace of the siphuncle is retained. 
Locality and horizon. — From the vicinity of Dayton, Ohio, at 
the base of the Whitewater member of the Richmond formation. 
Specimen No. 3082, in the Geological Museum of Ohio State Uni- 
versity. Along its upper margin the specimen contains a ventral 
valve of Rhynchotrema cayax. Traces of an incrusting bryozoan 
occur on one side of the specimen. 
Remarks. — Diestoceras eos differs from typical Diestoceras 
indianense in attaining the maximum enlargement of the conch 
at a point distinctly above the base of the living chamber. It is 
possible that the two species are identical, but, without a greater 
number of specimens at hand, it is not known within what limits 
Diestoceras indianense varies. The type of Diestoceras eos is so 
badly flattened as to leave elements of uncertainty, while that of 
Diestoceras indianense is much less distorted, and this species 
can be identified with confidence. For the present, at least, the 
latter is described as distinct. 
53. DIESTOCERAS SHIDELERI SP. NOV. 
PLATE XXVII, FIGS. lA, B 
Specimen presenting an elongate elliptical outline, consisting 
chiefly of a living chamber 55 to 58 mm. in height, with 4 cam- 
erae attached at its base. The specimen reaches its greatest 
transverse dimensions at mid-height of the living chamber. Here 
its lateral diameter is 67 mm., and its dorso-ventral diameter is 
63.5 mm. At the base of the living chamber' the corresponding 
diameters are 64 and 61 mm. respectively. At 50 mm. above the 
base of the living chamber the lateral walls curve strongly in- 
ward and then upward. Possibly this change in curvature indi- 
cates merely a thickened border in the interior of the chamber, 
