CLARK: TRENTON LIMESTONE AT MARTINSBURG. 15 



also two large specimens in a fragment of rock from Trenton Falls. 

 The matrix has on it the impression of a specimen of Phragmolites, 

 thus showing that these two forms occur together at Trenton Falls 

 as well as at Mardnsburg. 



Triplegia schucherti, sp. nov. 

 Plate 1, fig. 7-12. 



Shell large, of about the same size and shape as that of T. cuspidata, 

 but generally a little plimiper. The length and thickness are nearly 

 equal, the thickness equalling the length in some cases. The beaks 

 of the opposite valves are so closely opposed as to practically eliminate 

 a cardinal area. The brachial valve has a relatively narrow rounded 

 fold which does not project at the front, and which is bordered by 

 very shallow depressions. The fold is not so high and angular as in 

 either T. cuspidata or T. nucha, but more like that of T. extans. The 

 sinus in the pedicle valve is rounded at the bottom in the posterior 

 part of its course, but flat at the front and not deep. While this shell 

 attains the large size of T. cuspidata, it evidently resembled T. 

 extans in its younger stages, and is probably most nearly aUied to 

 that species. 



The surface is marked by both concentric and radial lines, the latter, 

 like those on T. exians, being most prominent toward the anterior 

 margin of the shell. Large specimens of both this species and T. 

 cuspidata often show obscure radial plications as well as striae. 



The type (M. C. Z. 8,534) selected as the best preserved of a dozen 

 specimens at hand, is 22 mm. long, 28 mm. wide, and 21 mm. thick. 

 A smaller specimen is 17 mm. long, 22 mm. wide, and 15.5 mm. 

 thick. The largest is 24 mm. long, 31 mm. wide, and 20 mm. thick. 



Seven of the specimens were collected by the writer from the base 

 of ]the Trenton at Martinsburg, and there are five more in the M. C. Z. 

 from the Trenton at Watertown, N. Y. 



Parastrophia rotunda (Winchell & Schuchert). 



Anasirophia? hemiplicata var. rotunda Winchell & Schuchert, Pal. Minn., 

 1893, 3, p. 383, pi. 30, fig. 32-35. 



While it is the common custom to refer all the forms of Parastrophia 

 found in the Trenton to one species, Winchell and Schuchert con- 

 ferred a varietal name on a very rotund form which they obtained 

 from the Galena (Prosser) limestone of Minnesota. I found in the 

 lowest Trenton at Martinsburg three specimens of an equally rotund 



