NO. 1^39. DEEP-WATER MOLLUSC A VEKHILL AND 7?r.<?77. 789 



forming a small, sunken, heart-shaped, lunular area. Posteriorly 

 there is only a faint, depressed undulation, which causes but a slight 

 indentation or angulation in the margin; behind this the surface rises 

 slightly and forms an inconspicuous ridge surrounding the ligamental 

 area, which is long, rather narrow, and sunken, so that its margin is 

 scarcely visible in a side view. The dorsal margin is a little convex 

 and slopes but little, and about equally on both sides of the beak; the 

 anterior end is well-rounded and slightly produced; the ventral margin 

 is broadly rounded, a little produced in the middle, and nearly straight 

 or very slightly incurved posteriorly, opposite the undulation; behind 

 this there is a slight obtuse angulation corresponding to the ridge below 

 the ligamental area. Surface dull grayish white. The hinge-margin is 

 considerably thickened, especially below the beaks and lunular area, 

 and a thickened ridge also extends backward beyond the ligamental 

 area. There is no distinct tubercle nor tooth-like projection. The 

 posterior ligament is unusually strong, and occupies a rather conspicu- 

 ous submarginal groove which runs forward under the beak as a thin 

 incised line. 



Length, 4 mm. ; height, the same. 



Found in 8 to 100 fathoms, north of Cape Cod, in the Gulf of Maine, 

 Casco Bay, Bay of Fundy, and Halifax Harbor, 1872-1885. 



CRYPTODON OBSOLETUS, new species. 



(Plate LXXXIX, figs. 1, 2.) 



Shell small, higher than long, with the ends and ventral margin 

 rounded. Umbos somewhat prominent and swollen; beaks cuived 

 strongly forward. Posterior plication obsolete, or nearly so, only 

 visible in certain positions, and imperfectly defined by a faint undula- 

 tion of the surface and margin. The antero-dorsal margin is slightly 

 convex in the lunular area, and slopes rapidly to the broadly rounded 

 anterior margin with which it forms a very slight and very obtuse 

 angle; the whole ventral margin is well-rounded, a little produced in 

 the middle; the postero-dorsal margin is broadly convex and ends 

 distally in a very obtuse, rounded angle, above which there is a slight 

 iubeuding of the edge. The hinge-plate is rather thick, especially pos- 

 teriorly. The ligament is rather strong and considerably curved and 

 occupies a narrow, but very distinct groove, mostly within the margin 

 posteriorly, and extends forward under and in front of the beaks. The 

 anterior hinge-margin is thickened and a little flexuous toward the 

 anterior angle of the shell; the proximal end, just under the beak, is 

 slightly thickened without forming any apparent tooth. Under the 

 microscope, the surface is covered with rather coarse, irregular, con- 

 centric undulations, and fine, raised lines of growth, becoming smoother 

 at each end, where there are patches of a closely adherent coating of 

 red mud and iron oxide. 



Length, 2.4 mm.; height, 2.0 mm. 



