244 THE VOYAGE OF H.M.S. CHALLENGER. 



paulo post medium maxime prominens. Umbones haucl acuti, ^jarum produc-ti, aute- 

 mediaiii. Linea cardinis gracilis, debilis, dentibus 8—9 utrinque instructa. Ligamentum 

 fuscesceus, brevis, partim externum, j^artim margiuale. 



This small species is very tliiu, rather convex, considerably inequilateral, of an 

 irregular ovate form, narrower in front than behind, white, very glossy, a little 

 iridescent, and sculptured with excessively fine lines of growth. The front dorsal slope 

 is short, the least convex, and a little oblique, the posterior being longer, also faintly 

 arcuate, but rather less sloping. The ventral outline is gently rounded, slowly up- 

 curving in front, and together with the dorsal margin forms a sharply i-ounded extremity. 

 The lower margin is most prominent a trifle behind the middle of the valves, and rises 

 posteriorly more suddenly than in front. The umbones are bluntly rounded, only 

 slightly elevated, and situated at about a third of the total length from the anterior 

 end. The hinge-plate is slender, and furnished with about eight or nine l)lunt-topped 

 teeth on each side, a small space under the beaks being edentulous. The ligament is 

 small, brown, partly internal in a small pit lieneath the umbones, and partly visible 

 externally, being located in a groove on the margin of the valves behind the beaks. 

 The interior is smooth, and the muscular scars are not clearly discernible. 



Length 4^ mm., height 3^, diameter 2^. 



Habitat. — Station 246, Mid North Pacific Ocean, in 2050 fathoms ; and Station 

 281, Mid South Pacific, in 2385 fathoms. 



The specimen from the latter locality apparently belongs to this species, differing 

 Ijut very slightly in lieing the least more strongly concentrically striated. In the 

 typical form of this genus, Sarepta speciosa, A. Adams, I also find a slight marginal 

 ligament besides the more distinct internal cartilage. 



Malletia, Desmoulins. 

 Malletia gigantea, Smith. 



Solenella yiganfea, Smith, Ann. and Mag. Nat. Hist., 1875 (July), ii. 72. 



Solenella ffigantea, Smith, Phil. Trans. Ro}'. Soc, 1879, vol. clxviii p. 187, pL ix. fig. 19. 



Habitat. — Betsy Cove, Kerguelen Island, in shallow water ; also at Balfour Bay, in 

 20 to 60 fathoms. 



A fine species, easily recognised by its large size, its form, and the few closely ranged 

 radiating strije upon the anterior side. 



Malletia arrouana, n. sp. (PI. XX. figs. 7-7b). 



Testa oblonga, subcpiadrata, valde intequilateralis, tenuis, convexa, antice oblic[ue- 

 curvata, postice arcuatim truncata, radiatim obsolete bisulcata, epidermide tenui dilute 



