430 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
lines of growth, without granulation or surface striation; form as figured ; inte- 
rior bluish white, slightly pearly; ligament and resilium combined, short, set 
obliquely, internally, under and behind the beaks; there is no lithodesma; hinge 
comprising one stout cardinal, prominent in the left valve entering a socket in the 
opposite valve in front of a long, nearly horizontal lamina, which forms the base of the 
resiliary pit; there is also one strong posterior left lateral, and a feeble anterior 
one on the same valve, which last is hardly to be distinguished from an angularity 
of the hinge margin ; pallial sinus wide, rounded, rather short. Length of shell, 
18; alt. 15; max. diam. 5 +6.5 mm., the smaller dimension being that of the 
left valve, which basally fits inside the other and has a slightly tortuous margin 
behind. 
U.S. S. “ Albatross,” station 8360, Gulf of Panama, in 1672 fathoms, sand, 
bottom temperature 42° F.; U. S. N. Mus. 122,942. Also at station 2793, off 
the coast of Ecuador, in 741 fathoms, mud, temperature 38°.4 F. 
This species, beside its much greater size, has beaks more inflated and higher, 
and the posterior end blunter than we find in P.'mactroides. 
Poromya (Dermatomya) chilensis Datt, n. sp. 
Shell small and rather thin, iridescent under a pale yellowish-olive periostracum ; 
valves subequal; inequilateral; anterior end shorter, narrower, rounded; poste- 
rior longer, wider, also rounded; beaks inflated but not very high; a single small 
ridge or angle extends from the beak to the lower posterior end of the shell, 
forming a posterior dorsal area over which the periostracum is darker and more or 
less wrinkled ; beaks three eighths of the total length from the anterior end; sur- 
face smooth and almost polished, except for faint incremental lines; interior 
pearly, pallial sinus shallow but wide and very distinct; hinge essentially as in 
the other species, but the cardinal long and slender, and the margins of its socket 
in the opposite valve prominent, almost like incipient teeth; the laterals are 
almost obsolete. Length of shell, 8; alt. 7.7; diam. 2.5 + 3.0 mm. 
U.S. S. “ Albatross,” station 2785, off the coast of southern Chile, in 449 
fathoms, mud, bottom temperature 47°F. U.S. N. Mus. 97,1385. 
This species has almost exactly the general form of Kedlia suborbicularis and is 
about the size of the average adult Kellia. The radial keel and rounded form 
separate it from the young of the other species. 
Another and still larger species than any of the above is found in deep water 
off the North Pacific Coast in about latitude 50°. 
CETOCONCHA Datt. 
Cetoconcha Dall, Bull. Mus. Comp. Zool., Sept., 1886, 12, p. 280; type, Lyonsva bulla 
Dall, Bull. Mus. Comp. Zool., 1889, 18, p. 452, pl. 39, figs. 2,5; Trans. Wag- 
ner Inst., 1895, 3, p. 586; Proc. U. S. Nat. Mus., 1889, 12, p. 289. 
Silenia E. A. Smith, Challenger Rept., 1885, Lam., p. 75; type, S. sarsii Smith 
(not Silenia Mulsant, Coleoptera, 1873). 
