300 
PALAEONTOLOGY OF NEW-YORK. 
Platyostoma veiitricosa. 
Plate LY. Fig. 9 a, b, c, d. 
Platyostoma ventiicosa : Conrad, Jour. Acad. Nat. Sciences of Philadelphia, 1842, Yol. viii, pa. 275, 
pi. 17, f. 5. 
“ Globose : whorls somewhat scalariform, or flattened above ; lower part 
“ of columella prominent; labrum reflected; width and length of 
“ aperture nearly equal.” 
The specimens before me vary from globose to depressed-globose, and obliquely 
ovoid; due perhaps in part to the original form of the shell, and more to the sub¬ 
sequent accidental causes. After comparing a large number of specimens, I do not 
find ally constant or satisfactory character for the reliable separation of those occur¬ 
ring in the Oriskany sandstone, from those in the Lower Helderberg group, which 
seem to me referable to this species of Mr. Conrad. 
The Platyostoma arenosa of Conrad ( Trans. Acad. Nat. Sciences of Philadelphia, 
Yol. viii, pa. 276, pi. 17, f. 6 ) appears to me to be only the young of P. ventricosa. 
Some of the speciinens from the Oriskany sandstone, of the same dimensions as the 
figure cited, do not differ from that one; while there are numerous intermediate 
forms, which, in the casts, cannot be satisfactorily distinguished. 
As this fossil appears in its various forms, it may be described as Globose, more 
or less depressed or obliquely subovoid : spire moderately elevated, consisting of 
three or four volutions, the last one of which is extremely ventricose ; volutions 
flattened upon the upper side; aperture circular or subovate; columellar lip re¬ 
flexed. Surface marked by fine closely arranged striae. 
Fig. 9 a. Yiew of a depressed-globose specimen, from which the shell is nearly removed. 
Fig. 9 b. Yiew of the aperture of the same. [ This figure is not properly given.] 
Fig. 9 c. A globose specimen which preserves a fragment of the shell. 
Fig. 9 d. A worn specimen, showing a longitudinal section of the shell on one side of the 
centre. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Catskill, and Becraft’s mountain. 
