780 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



A few separate valves, off Cape Hatteras, North Carolina, in 10 to 17 

 fathoms, 1884. 



MONTACUTA BIDENTATA (Montagu), variety FRAGILIS, new. 



(Plate XCII, fig. 8.) 



Shell subelliptical, inequilateral, both ends broadly rounded, thin, 

 fragile, covered with delicate lines of growth. The umbos are flat- 

 tened; beaks but slightly prominent. The teeth in the right valve are 

 smaller and more delicate than in the typical bidentata, and diverge 

 but slightly from the dorsal margin, as in that species. 



Length, 4 mm.; height, 3 mm. 



One specimen (No. 40134), station 816-17, in Narragausett Bay, in 

 8i to 10 fathoms, 18SO. 



MONTACUTA STRIATULA, new species. 

 (Plate XCIII, tig. 9.) 



Shell rather large, thin and somewhat hyaline, compressed, broad- 

 elliptical with both ends well rounded, the anterior much the longer. 

 Antero-dorsal margin nearly straight with a gradual slope; anterior 

 end broadly and regularly rounded, its outline forming nearly the seg- 

 ment of a circle; ventral margin broadly and evenly convex; posterior 

 end bluntly rounded with its dorsal margin slightly concave and slop- 

 ing rapidly. Umbos not swollen; beaks acute and only a little promi- 

 nent. Surface covered with fine, regular, concentric, microscopic stria- 

 and more distant lines of growth. Interior somewhat shining with 

 inconspicuous muscular scars. Hinge-margin thin, delicate, only 

 slightly thickened. In the right valve there is, on each side of the 

 beaks, a short, rather delicate, elevated, triangular tooth, terminating 

 distally with an abrupt slope; these are nearly equal in size and length, 

 the anterior one being slightly the shorter and more angular. They are 

 separated by a V-shaped notch, the sides of which form nearly a right 

 angle. In the left valve there are two thin, slightly prominent eleva- 

 tions, scarcely worthy the name of teeth, separated by a very wide 

 angle under the beak. 



Length of one of the largest specimens, 7 mm.; height, mm. 



This species is much larger than any of our other species of this 

 genus, and may possibly prove to be identical with M. bowman i, 

 described and figured by Holmes. 1 Owing, however, to the shortness 

 of the description and small size of the figures, this question cannot 

 be definitely decided without a careful comparison with authentic 

 specimens. 



A few separate valves were found off Cape Hatteras, North Caro- 

 lina, in 15 to 48 fathoms, 1883-84. 



1 Post-pleioceiie fossils of South C'arolinu, p. 30, pi. VII, fig. 2, 1860. 



