2183. NEW NORTHWEST AMERICAN BIVALVES— BALL. 409 



THYASIRA CYGNUS, new species. 



Shell white with a pale straw-colored periostracmn, moderately 

 convex, sharply compressed behind, the beaks prommeiit, prosocoe- 

 lous over a large cordate Imiule, the escutcheon long and very narrow, 

 bomided by a sharp keel; general form romided quadrate, the com- 

 pressed posterior area narrow and basally falling notably short of the 

 basal curve of the disk; posterior slope sUghtly convexly arcuate; 

 anterior distmctly concave, meeting the basal arc m an obtuse angu- 

 lation. Length, 14; height, 13.5; diameter, 8.5 mm. Cat. No. 

 222618, U.S.N.M. 



Station 4224, Cygnet Inlet, Boca de Quadra, Alaska, in 160 fathoms. 



THYASIRA TRICARINATA, new species. 



Shell chalky white, produced below, with pointed prosocoelous 

 beaks over a deeply impressed ovate lunule bounded by a sharp 

 carina; escutcheon long, narrow, lanceolate, the valve margins rising 

 as a sharp keel in the middle, the outer border very prominently 

 keeled, outside of which is a similarly shaped excavated area also 

 bordered by an angular keel; still outside of this there is a com- 

 pressed area with no distmct anterior boundary except an obscure ray 

 near the umbones ; over this area the surface is concentrically striated, 

 the rest of the disk bemg nearly smooth; hinge very feeble, ligament 

 linear. Length, 15; height, 18; diameter, 10 mm. Cat. No. 209321, 

 U.S.N .M. 



Station 4425, off the Santa Barbara Islands, California, in 1,100 

 fathoms. 



ERYCINA CATALINAE, new species. 



Shell small, inequilateral, the anterior side shorter, rounded, the 

 base nearly straight; posterior side also romided, sUghtly attenuated, 

 the dorsal slope convex but descending; hinge strong, the teeth well 

 developed; the beaks well developed, not prominent, the surface 

 smooth except for faint incremental lines, covered with a light yel- 

 lowish-brown dull periostracum. Length, 2.5; height, 2; diameter, 

 1.3 mm. Cat. No. 210879, U. S.N. M. 



Catalina Island. California, Brannan. 



ERYCINA? CORONATA, new species. 



Shell small, white, rounded quadrate, nearly equilateral, the surface 

 finely concentrically striated; basal margin nearly straight; ends 

 rounded, the posterior a little produced basally, the dorsal slopes 

 similar, sHghtly descending, with at each end two to four mmute ele- 

 vated spinules. Length, 4; height, 3; diameter, 1.2 mm. Cat. No. 

 225193, U.S.N.M. 



Off South Coronado Island, in 3 to 6 fathoms. Dr. F. Baker. Only 

 one left valve was obtained. 



