430 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



lines of growth, without granulation or surface strialion ; form as figured ; inte- 

 rior bluish white, slightly pearly ; ligament and resilium combined, short, set 

 obUquely, 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 

 resihary 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, 

 IS; 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 3360, Gulf of Panama, in 1672 fatlioms, sand, 

 bottom temperature 42° F. ; TJ. S. N. Mus. 122,9-42. Also at station 2793, off 

 tlie 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 Dall, n. sp. 



Shell small and rather thin, iridesceut 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 eud of the shell, 

 forming a posterior dorsal area over which the ppriostracum 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. 7J ; 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. 97,135. 



This species has almost exactly tlie general form of Kellia suborbiculari* 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°. 



CETOCONCIIA Dall. 



Cetoconrha Dall, Bull. Mus. Comp. Zool , Sept., 1886. 12. p. 280 ; type, Lyonsia huUa 

 Dall, Bull. Mus. Comp. Zo<.l., 1889, 18, p. 452, pi. 39, figs. 2, 6 ; Trans. Wag- 

 ner Inst., 1895, 3, p 530; Proc. U. S. Nat. Mus., 1889. 12, p. 289. 



Silenia E. A. Smith, Cliallenger Rcpt., 1885, Lam., p. 76; type, 5. sarsii Smith 

 (not Silenia Muisant, Coleoptera, 1873). 



