AMERICAN PALEOZOIC CEPHALOPODS " 265 
size, and the convexity of the vertical outlines of its segments ; 
but the siphuncle has broken loose from the septa, and the struc- 
ture of the siphuncle can not be determined in a satisfactory 
manner. 
Saluda and Elkhorn specimens. — Specimens from the Saluda 
and Elkhorn members of the Richmond are in the collection of 
Prof. W. H. Shideler. These specimens evidently are congeneric 
with Diestoceras indianense , but not enough of the conch is pre- 
served to make certain that they belong to the same species. One 
of these Salula specimens (Plate XXVII, Fig. 2) preserves the 
surface striae very well. 
52. DIESTOCERAS EOS (HALL AND V^HITFIELD) 
PLATE XXVIII, FIGS. lA, B 
Gomphoceras eos Hall and Whitfield: Geol. Surv. Ohio, Pal., vol. 2, 
1875, p. 100, pi.' 3, fig. 5 
'‘Type. — Specimen 112 mm. in length; of this length 65 mm. 
belongs to the living chamber, 36 mm. belong to that part of the 
phragmacone which occurs between the base of the living 
chamber and the suture of the septum at the base of the speci- 
men, and 11 mm. belongs to that part of the specimen which 
extends below the level of this suture in consequence of the down- 
ward curvature of the septum. 
In its present condition the specimen is very much crushed 
laterally. The maximum expansion of the conch takes place 
about 23 mm. above the base of the living chamber. Here the 
dorso-ventral diameter is 81 mm., and the lateral diameter is 
36 mm. At the base of the living chamber the corresponding 
diameters are 74 and 30 mm. At the base of the specimen these 
diameters are 44 mm. and 19 mm. The apical angle of that part 
of the phragmacone which is preserved approximates 45°. Above 
mid-height of the living chamber the latter contracts so that 
at 55 mm. above its base the dorso-ventral diameter is 62 mm. 
and the lateral diameter 21 mm. Above this level the living 
chamber continues to contract until its dorso-ventral diameter 
does not exceed 55 mm. 
It is assumed, from the better preserved specimens of Diesto- 
ceras indianense, that the cross-section of Diestoceras eos orig- 
inally was nearly circular, and that the outline of the aperture 
was nearly circular, with a moderate amount of angularity along 
the ventral margin. In conformity with other species referred 
