ORISKANY SANDSTONE. 
469 
incipient tortuous columella, one or two specimens approach the Genus 
Strophostylus. 
Although the discrimination of species is attended with some difficulty 
when few specimens are examined, there has nevertheless appeared, in 
the large collections obtained, sufficient reason to regard the species 
indicated as well established. 
Platyostoma ventricosa. 
Plate CXII. Fig. 1-10; Plate CXIII. Fig. 7 & 8 ; and Plate CXV. Fig. 8 . 
Platyostoma ventricosa : Conrad, Jour. Acad. Nat. Sci. Philadelphia, Vol. viii, pa. 275, pi. 17, f. 1. 
— — This volume, pa. 300, pi. 55. 
Shell globose or depressed-globose and often obliquely ovoid, varying in 
form. Spire moderately elevated, consisting of three or four volutions, 
the last of which is extremely ventricose : volutions flattened upon 
the upper side; aperture circular or subovate; columellar lip reflexed. 
Surface marked by fine closely arranged striae parallel to the lines of 
growth. 
The surface is sometimes marked by broad undulations, both in young and in old 
shells; but I am not able to find in these forms any means of specific distinction. 
PLATE CXII. 
Fig. 1 & 2. Young shells of this species. 
Fig. 3. A young specimen, showing a broad undulating surface. 
Fig. 4 a. View of the aperture of the same. 
Fig. 4 b. An older specimen of the ordinary form. 
Fig. 5 a, b. View of the spire, and of the aperture of a specimen of medium size. 
Fig. 5 c. Profile of a specimen which is somewhat depressed vertically. 
Fig. 6. A young specimen with a more elevated spire. This is of the type of P. arenosa of 
Conrad (See page 302, this volume). 
Fig. 7 & 8. View of the spires of two specimens of ordinary form. 
Fig. 9. A specimen which has been vertically compressed. 
Fig. 10 a, b. Yiew of a specimen which is a little compressed obliquely. 
PLATE CXIII. 
Fig. 7. Profile of the spire of a very large specimen, which has been somewhat compressed 
vertically. 
Fig. 8. Yiew of the spire of the same specimen. The surface shows broad undulations pa¬ 
rallel to the lines of growth. 
