386 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



The pallial sinus is notable in that the greater part of its basal scar is identical 

 •with the pallial line itself, whereas in most of the Malletinae the sinus tends to 

 slope obliquely upward. 



Malletia (Minormalletia) benthima Dall, n. sp. 



Plate 15, figures 1, 2. 



Shell small, thin, earthy, covered with a polished, thin, grayish periostracum ; 

 very inequilateral, bluntly rounded in front and behind ; beaks pointed, recurved, 

 prominent ; situated at the anterior third ; surface smooth, except for lines of 

 growth and very sparse, faint, radial striatious which appear confined to the peri- 

 ostracum ; posterior hinge line and base nearly parallel ; ligament very delicate, 

 ampliidctic but mostly behind the beaks ; resilium minute, obscure, not inter- 

 rupting the line of teeth ; anterior teeth 12-13, posterior 17-18, small and closely 

 crowded ; interior earthy, polished, the muscular scars pronounced, small ; pallial 

 sinus large, deep, rounded behind, reaching nearly to the middle of the shell, 

 rising obliquely from the entrance ; no lunule or escutcheon. Beaks in front of 

 the posterior end, 6.5; anterior end of sinus, 4.5; total length, 9.5; alt. 5.3; 

 diam. 4.0 mm. 



U. S. S. " Albatross," station 3417, off Acapulco, Mexico, in 493 fathoms, 

 mud, bottom temperature 40°.6 E. U. S. N. Mus. 122,927. 



A very plain and simple but rather peculiar looking species. 



NEILO A. Adams. 



Malletia Nelro) goniura Dall. 



Plate 18, figure 6. 



Malletia goniura Dall, Proc. U. S. Nat. Mus., 1889, 12, p. 251, pi. 10, flg. 10. 



Shell extremely thin and fragile, translucent whitish, covered with a rather 

 dark olive periostracum, smooth and polished ; beaks low, adjacent, nearest the 

 anterior end of the shell, witli a linear lunule and escutcheon, a long and strong 

 external ligament but no internal resilium ; anterior dorsal slope arcuate, short, 

 passing insensibly into the curve of the evenly rounded anterior end ; posterior 

 longer, straight, ending in an obtuse angle at the posterior truncation ; a single 

 elevated small thread or keel extends from each beak to the lower posterior 

 margin of the valve, above which the valve is somewhat excavated ; the upper 

 border of this trougli or excavation is slightly prominent, tliough n(4 indicated 

 by a keel, and tlie margin between the radial thread and this prominence is 

 somewhat concave, produced at the end of the prominence and Ihonce obliquely 

 truncate to the dorsal margin, which is compressed ; the posterior end of the 

 shell, except for the undulation mentioned, is abruptly truncate and meets the 



