782 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



MONTACUTA CUNEATA, new species. 

 (Plates XCI, fig. 4; XCIII, fig. .".) 



Shell small, elongated, wedge-shaped, with a much produced, narrow 

 anterior end, and with the dorsal margins nearly straight, sloping rap- 

 idly, and forming an obtuse angle at the beaks, which are decidedly 

 behind the middle, prominent, curved inward. Antero dorsal margin 

 sloping rapidly, at first nearly straight, becoming a little convex, and 

 curving regularly into the ventral margin, thus forming a somewhat 

 rostrated, narrow, evenly rounded anterior end; ventral margin nearly 

 straight, sometimes with a slight incurvature opposite the beaks ; poste- 

 rior end bluntly rounded, with its dorsal margin nearly straight, sloping 

 about equally with the anterior. The surface is covered with fine, con- 

 centric, rather regular lines of growth and microscopic striations. Inte- 

 rior somewhat shining. In the right valve there are two well defined, 

 prominent, thickened teeth, separated by a large, deep notch under the 

 beak; the anterior one is the larger and is broadly triangular, with a 

 prominent excurved tip, and is separated from the hinge-margin by a 

 deep furrow, which runs obliquely within and below the thickened dorsal 

 margin; the posterior one is set obliquely to the margin, from which it 

 is separated by a well defined groove. In the left valve there is a wide 

 notch beneath the beak, with a rather inconspicuous, elongated, some- 

 what thickened anterior tooth-like projection, which continues forward 

 as a thickened inner margin nearly to the end, and a shorter, broad, 

 triangular posterior projection. Color cream-white, sometimes tinged 

 with pink. 



Length of the largest specimen, about 3 mm.; height, l.~> mm. 



A few specimens were found off Cape Hatteras, North Carolina, in 

 15 and 1(3 fathoms, 1883-84. 



MONTACUTA TRIQUETRA, new species. 

 (Plnte XCI, fig. 3.) 



Shell small, covered with regular concentric grooves, scarcely corn- 

 pressed, somewhat triangular, with a slightly rostrated, angular posterior 

 end, and a regularly rounded anterior one. Umbos a little swollen, 

 beaks nearly central, pointed and a little prominent. The anterior and 

 posterior dorsal margins form nearly a right angle; the anterior margin 

 is slightly convex and passes gradually into the somewhat bluntly 

 rounded anterior end; ventral margin broadly convex, becoming 

 slightly incurved toward the posterior rostratiou, which is wedge- 

 shaped, rapidly tapered, with a narrow truncate tip, defined below by 

 a faint, radiating ridge; postero-dorsal margin is nearly straight, and 

 slopes rapidly from the beaks. The surface is sculptured with strongly 

 marked, smooth, rounded, concentric ridges having the upper edge 

 smooth and recurved; these are separated by deep, regular grooves 



