854 PELECYPODA. [Filibranchia. 



The dorsal area is narrow, elongate-elliptical, rather deeply concave, 

 of a light-brown colour, and provided with a diamond-shaped central 

 dark-brown ligament. 



Length, 8-5 mm. ; height, 8-5 mm. ; diameter, 4-7 mm. 



Type in the British Museum. 



Hub. " Challenger " Station 169, off the north-east coast of New 

 Zealand, in 700 fathoms 



Remarks. This little species is peculiar for its width, comparative 

 solidity, and dentate margin, and bears considerable resemblance to 

 L. minuta, Philippi. 



Genus 2. LISSARCA, E. A. Smith, 1877. 



Lissarcn, E. A. Smith, Trans. Venus Exp. Kerguelen, Moll., 1877, 19. Type : 

 L. rubrofusca, E. A. Smith. Austrosarepta, Medley, P.L.S. N.S.W., 

 1899, 430. 



Shell equivalve, very inequilateral, umbones anterior ; sculpture 

 concentric, and frequently radial in addition ; with an amphidetic 

 internal ligament and a central resilium ; hinge-line arched ; teeth 

 few, more or less distinctly > -shaped, an edentulous hiatus in the 

 middle ; a number of crenulations on the anterior margin. 



Distribution. Antarctic. 



KEY TO SPECIES. 



A. Shell ovate ; colour purplish-red or brown. 



a. Valves convex, but not inflated, with tine radial stria 1 . . aucklandica, 

 aa. Valves ventricose, with tine radiate riblets . . . . pisuni. 



B. Shell transversely trapezoidal ; colour light brown or yellowish ; 



beaks close to the anterior end . . . . . . exilis. 



}. Lissarca aucklandica, E. A. Smith, 1902. Plate 51, rigs. 10, 10.. 

 iiHflcliuidica, Smith, Rep. on Collect. Nat. Hist. " Southern Cross," 



Moll., 1902, 212, pi. 24, f. 14, 15. 



Shell small, equivalve, very inequilateral, convex, purplish-red, 

 almost smooth. Beaks not very prominent, approximate, but not 

 quite contiguous, near the anterior end. which is short and broadly 

 rounded ; the posterior end with the dorsal margin slightly raised 

 and convex, the posterior margin sloping, lightly convex, narrowly 

 arched towards the convex basal margin. Cardinal area very narrow. 

 Scn.lpt.ure consisting of fine and dense growth-lines, sublamellar pos- 

 teriorly, and faint fine post-median radiate stripe. Colour uniformly 

 purplish-red. Interior of the same colour, with faint posterior radiate 

 strife, not shining. Margins strongly denticulate inside, except on 

 the antero-ventral and the posterior median parts. Hinge-plate 

 narrow, arcuate, smooth in the middle, with 4 to 5 short anterior 

 and 4 V-shaped posterior teeth. Ligament very small. Adductor-scars 

 unequal, the posterior one longer. Pallial lin>- simple. 



Length, 4-5 mm. ; height, 3-5 mm. ; diameter, 2-3 mm. (type). 



