GASTEROPODA. 
25 
Platyostoma euomphaloides. 
PLATE X, PIGS. 27-29. 
Platyostoma euomphaloides, Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 9. 1876. 
Shell depressed subhemispheric ; spire moderately elevated ; volutions three 
or four, gradually enlarging from the apex,—the last one expanded, 
not ventricose, with its exterior or periphery flat or slightly convex, 
and flattened or gently concave in the middle above; suture-line 
close. Aperture expanded, broadly subovoid ; the inner lip has a 
thickened callus, which projects in a prominent rim along the posterior 
border of the aperture. 
Surface marked by fine concentric striae, which are crowded in fascicles. 
At present, we know only a single specimen having the character described. 
The flattened upper side of the volutions and the flattened periphery are very 
unlike any form of Platyostoma described, but at the same time it is not difficult 
to see how a still farther degree of variation in P. lineata var. callosa may 
result in such a form as this. In that variety, the summit is depressed, but 
the volutions are rotund and rapidly expanding, with an aperture suborbic- 
ular. Unlike the prevailing or characteristic forms of P. lineata , that one has a 
thickened callosity on the inner lip, but less defined and developed than in the 
specimen described as P. euompholoides. 
Platyostoma Strophius. 
Platyostoma Strophius, Hall. Descriptions of New Species of Fossils, etc., p. 13. 1861. 
“ “ “ Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 41. 1862. 
Shell obliquely ovoid. Apex minute; spire ascending, composed of about 
three or four volutions, very gradually expanding above; the bodv- 
whorl ventricose, somewhat depressed-convex on the side, and sloping 
downward rather than swelling out in a rotund form ; the upper volutions 
standing out prominently above the last one. Suture-line narrow, even, 
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