GASTEROPODA OF THE MIDDLE GKEEN MAELS. 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 Whitf 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 Solarium 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 iiaterual cast, I should sup- 



