382 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
polished; interior chalky, with a shallow but distinct pallial sinus; hinge with 
about nine anterior and ten or eleven posterior teeth between which the minute 
resilium is set apparently directly on the edge of the valve, no pit or chondro- 
phore being visible under a lens. Length of shell, 5.0; of anterior end, 2.5; 
alt. 3.2; max. diam. 2.5 mm. 
U.S. S. “ Albatross,” station 2792, in 401 fathoms, mud, off Manta, Ecuador, 
bottom temperature 42°.9 F. U.S. N. Mus. 122,756. 
Yoldia (Yoldiella) granula Da t, n. sp. 
Shell minute, oval, equilateral, moderately tumid, smooth, covered with a 
polished straw-colored periostracum; interior porcellanous, with a very slight 
pallial sinus and smooth margins ; hinge line with about six teeth on either side 
of a well-developed resilium, the most anterior tooth of alla little more distant 
and notably larger than any of the others. Length, 1.7; alt. 1.2; max. diam. 
1.0 mm. 
U. S. 8S. “ Albatross,” station 2778, in Magellan Straits, in 61 fathoms, bottom 
temperature 47°.9 F. U.S. N. Mus. 110,693. 
Only a single valve was obtained of this very minute species, but the solidity 
of the specimen indicates that it is not the fry of one of the above described 
larger species. 
Yoldia (Yoldiella) dicella Datz, n. sp. 
Shell small, solid, chalky-white, covered by a dark olive dull periostracum, 
slightly inequilateral, with low, adjacent beaks; of oval form, and with neither 
lunule nor escutcheon; anterior end broadly rounded, posterior narrower and 
longer, but also rounded, base evenly arcuate; surface nearly smooth at the um- 
bones, but feebly concentrically striated on the disk, especially the lower part of it; 
without any radial sculpture; interior chalky-white, the margins entire, the mus- 
cular scars distinct, the pallial line with a shallow, hardly angular sinus; hinge 
line with about ten anterior and fifteen posterior small crowded teeth, separated by a 
deep pit occupied by the entirely internal resilium. Lon. of shell, 6; of beaks 
behind the anterior end, 3; alt. 4; diam. 3 mm. 
U. 58.5. “ Albatross,” station 3418, off Acapulco, Mexico, in 660 fathoms, sand, 
bottom temperature 39° F. U.S. N. Mus. 122,917. 
This little spade-shaped species is clearly distinct from any of the others con- 
sidered in this paper. 
Yoldia (Yoldiella) leonilda Da t, n. sp. 
Shell small, smooth, oval, subequilateral, plump, white, covered with a polished 
pale straw-colored periostracum; beaks low, eroded, slightly nearer the anterior 
