GASTEROPODA OF THE MIDDLE GREEN MARLS. 179 
The species is rather a marked one, and so distinct from any other 
shell or cast known from the American Cretaceous formations that it will 
not be readily mistaken. In form and size it distantly resembles Mar- 
garitella Abbotti Gabb, but has a lower spire, more rapidly increasing and 
less numerous volutions, and by being nodose above and below will be 
readily distinguished from that shell. I am greatly in doubt as to the 
locality of this specimen. I am assured that it is from the locality cited 
below, but it so closely resembles specimens from the Rhone in France 
that I have been inclined to reject it altogether; and have admitted it only 
with the hope that it may be verified by the discovery of additional 
specimens. 
Formation and locality: In a rather light colored marly limestone, with 
scattered grains of glauconite. It is said to have come from the Middle 
Marls at Tinton Falls, New Jersey, and is from the collection at Colum- 
bia College. Collected by Dr. Britton. 
PLEUROTREMA, n. gen. 
Shell solarium-like in general form, but without angulation to the 
inner basal margin of the volutions bordering the umbilical cavity, but 
somewhat regularly curving from the middle of the base to the upper inner 
margin, giving a broad funnel-formed umbilical cavity. Periphery marked 
in the place of the notch in Pleurotomaria by a series of oval perforations 
similar to those of Polytremaria D’Orb. Type P. solariformis Whitt. Cre- 
taceous. 
I know but a single species of this genus, that described below, but 
the combination of characters are so peculiar that I do not like to place it 
under any known genus. The general from is like that of Solariwm Lamarck 
(Architectonica, Bolt), but is widely distinctive in the peculiar form of the 
umbilicus and in the perforations of the outer portion of the whorl. In this 
latter feature it approaches both Pleurotomaria and Polytremaria. From the 
first it differs in having the slit divided into a series of oval openings, and 
from the last materially in the subrhomboidal form of the volutions and in 
the form of the broadly open and funnel-shaped umbilicus. From the 
appearance of the nodes and ridge left on the internal cast, I should sup- 
