802 
PALAEONTOLOGY OF NEW-YORK. 
Platyostoma arenosa. 
Plate LYII. Fig. 3 a , b. 
Platyostoma arenosa : Conrad, Jour. Acad. Nat. Sciences of Philadelphia, 1842, Yol.viii, pa. 276, 
pi. 17, f. 6. 
“ Obliquely ovate-globose : body-whorl rapidly widening to the base ; 
“ aperture longitudinally suboval.” 
The above description of Mr. Conrad corresponds with the characteristics of this 
and other specimens in my collections, which, however, appear to me as the young 
of P. ventricosa . As the specimens are mostly casts, or only preserving the shell in 
a very imperfect condition, it is impossible to determine this question at the present 
time with entire satisfaction. 
Fig. 3 a. View looking upon the spire. Fig. 3 h. View of the aperture of the same. 
Geological position and locality . In the slialy limestone of the Lower Helderberg 
group : Near Catskill. 
There are, besides the true Platyostoma, some other shells of not very 
dissimilar character in the rocks of this age. Some of these, in the casts 
and in their exterior conformation, are remarkable for their oblique form 
and the wide-spreading of the last volution, which is also often exagge¬ 
rated by pressure in the same direction. 
These fossils have sometimes the globose form of Platyostoma ; but in 
these instances they are usually more symmetrical, and may be recognized 
by the smoothly rounded outline and the extreme posterior extension of 
the outer lip on the adjacent volution. The surface is evenly striated by 
fine elevated threadlike striae parallel to the lines of growth. 
Although differing in external characters from any other gasteropods 
of the group, I have not until recently had the means of determining the 
generic relations of these forms. During the past year (1857) I obtained 
from Mr. Andrews of Cumberland, Maryland, some Gasteropoda of the 
Oriskany sandstone, among which was a single specimen of one of these 
shells entire and without adhering stone. This specimen, and some others 
