434 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Shell small, thraciaeform, smooth, polished, greenish white, inequivalve, nearly 
equilateral, briefly rostrate ; right valve larger, convex, rounded in front; beaks 
small, prominent, slightly incurved; neither lunule nor escutcheon present ; 
posterior end strongly and suddenly compressed, the compressed portion bounded 
in front by a depressed ray extending from the beak to the posterior basal 
margin ; posterior end short and rounded, somewhat narrower than the anterior ; 
left valve similar but smaller and less convex, at the posterior hinge line under- 
lying the margin of the right valve ; hinge with a small roundish projecting chon- 
drophore which extends under the margin of the left valve to which it is united 
by the resilium ; there is no ossiculum; the periostracum is papery and caducous, 
visible chiefly at the posterior and basal margin. Lon. 6.0; alt. 4.5; diam. 
2.7 mm. 
U. S. 8. “Albatross,” station 4654, twenty-four miles N. 68° W. of 
Aguja Point, Peru, in 1036 fathoms, mud, bottom temperature, 37°.3 F. U.S. 
N. Mus. 110,582. The original type was obtained on the southwest coast of 
Chile, at station 2791, in 677 fathoms, mud, bottom temperature, 37°.9 F. 
The specimen was badly smashed, but it was possible to determine, that it, in 
all probability, belonged to this species. 
WMWONERA Dat. 
Myonera garretti Datt, n. sp. 
Plate 5, figure 4. 
Shell extremely thin, white, polished, with a pale straw-colored periostracum, 
of general corbuloid form, and edentulous hinge ; valves convex, compressed sud- 
denly behind; anterior part convex, with about fifteen concentric sharp ripples, 
with much wider interspaces ; these ripples start from the anterior margin, on the 
upper half of the disk, are obsolete on the dome of the valve; near the margin 
they extend further back, nearly reaching the first radial rib; the remaining 
concentric sculpture is of fine lines of growth over the whole surface ; the radial 
sculpture consists of, on the left valve, a single strong radial rib extending from 
beak to basal margin and bounding in front the compressed triangular rostrum ; 
on the right valve there is a weak rib separated by a wide, shallow, excavated 
channel or trough, from a second strong rib corresponding to that of the oppo- 
site valve; there is no lunule or distinct escutcheon, but the pointed, short, pos- 
terior, compressed end of the shell is triangular, bluntly rounded off at the 
extremity, rostrate, and a little flexuous; ligament thin, elongate; resilium 
short, with a narrow rather long rectangular ossiculum ; the interior polished, 
the scars invisible; margins entire, except a small prominence at the end of the 
radial ribs. Lon. 18.5; alt. of shell, 11.0; of beaks, 1.5; diam. 9.0 mm. 
U. S. 8. “ Albatross,” station 3380, southeast from Malpelo Island, Gulf of 
Panama, in 899 fathoms, hard bottom, temperature 37°.2 F. U.S. N. Mus, 
122,941. 
