130 PALEOZOIC PALEONTOLOGY. 
POLYGYRATA n. gen. 
Shell depressed-conical, with many non-embracing volutions, whose 
cross-sections are rhomboidal. The umbilicus broad and open, its 
sloping sides subparallel with the sloping sides of the spire. The 
genus probably includes both sinistral and dextral species. Type of 
the genus P. sinistra. 
POLYGYRATA SINISTRA N. §p. 
Plate IV:, Figs. 1-2. 
Description.—Shell large, sinistral, depressed, conical. Volutions 
many, slightly elevated at the suture, not at all embracing. Umbilicus 
broad and open, its sloping sides subparallel with the sloping sides 
of the low spire. Cross-section of the volution rhomboidal, the width 
being twice the depth. 
Maximum diameter of the type specimen, 37 mm. 
Remarks.—The most perfect specimen of this species in the collec- 
tion has been used for the construction of the diagrammatic illustra- 
tions here presented. In the vertical view the sutures actually pre- 
served are represented by the full lines, the broken lines indicating 
the portion which has been supplied. On one side the specimen is 
broken in such a manner as to exhibit a cross-section of several volu- 
tions, and from this the cross-section of the shell here presented has 
been constructed. 
This species resembles Huomphalus polygyratus Roem.,* from the 
lower Ordovician (?) of Texas, but differs from it in being a sinistral 
shell and in having the cross-section of the volutions much broader. 
The two species described by Meek} from the lower Ordovician of 
Utah, under the names Raphistoma? rotuliformis and Raphistoma? 
trochiscus, are also similar shells, but, ike 2. polygyratus, both have 
dextral spires, and they are much smaller than either the Texas or 
New Jersey shells. Plewrotomaria hunterensis Cleland, from neay 
Fort Hunter, New York, is another species of this group which re- 
sembles the New Jersey shell quite closely, but is coiled in a dextral 
* Die Kreidebildungen von Texas (1852), p. 91, pl. XL, figs, 4a—40. 
7 U. S. Geol. Expl., 40th par., pp. 18, 19, pl. L., figs. 2-3. 
. 
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