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



Hahiiat. — Station 237, off the south-east of Nipou, Japan, in 1875 fathoms. 



This is quite distinct from all the known species of Malletia, and is the only one at 

 present known from Japanese Seas. I have named it after the late Dr. W. Dunker, 

 author of several papers and valuable works on the Mollusca of Japan. 



Leda ultima, n. sp. 



Testa minuta, ovato-subtriangularis, convexa, antice rotundata, postice angustata, 

 subrostrata, ilavescens, parum nitida, liris tenuibus concentricis confertis regularibus 

 sculpta. Margo dorsi utrinque ajqualiter deelivis, antice vix curvatus, postice rectus. 

 Margo inferior late arcuatus, extremitatem posticam versus ad termiuum impressionis 

 lataj ab umboue radiantis incurvatus. Umbones albi, Iseves, centrales, involuti, haud 

 acuti. Liuea cardinalis crassa, dentibus cii'citer sex utrinque iustructa. 



This little species is rather thick in texture, considerably convex, ovate but 



narrowed at the hinder end into a short rostrate extremity. It is white, clothed with 



pale straw-coloured epidermis except at the umbones, which consequently 



appear white, and are smooth, central, slightly prominent, rather obtuse 



and incurved at the tip. The valves are marked with a distinct broad 



, , „. radiating depression down the posterior side, and sculptured with 



LccUt ultima, n. sp. o -^ ^ ' >- 



numerous regular fine close-set concentric lirje which become more slender 

 at the sides. The dorsal line is considerably sloping on both sides, the least excurved 

 in front, straight at first behind the beaks, then down-curving to the sharpish rostrate 

 extremity. The ventral margin is well curved in front and along the middle portion 

 of the valves, but distinctly sinuate at the termination of the oblique impression. The 

 hinge-plate is very strong and broad for so small a species, and furnished with six 

 or seven teeth on each side the small central triangular ligamental pit. The interior is 

 glossy, and exhibits distinct deep muscular scars. 



Length 2|- mm., height 2, diameter 1:^. 



Habitat.— ^l^tion 5, February 21, 1873; hit. 24° 20' N., long. 24° 28' W.; south- 

 west of the Canary Islands ; depth, 2740 fathoms ; bottom, red clay. 



Leda messaneiisis is more sharply beaked behind than this species, more finely 

 sculptured, more narrowly rounded in front, and has a less distinct oblique impression 

 down the posterior side. Leda semen is about the same size but more elongate, 

 has finer strise and a fainter depression. 



Leda confinis is narrower, smoother, less equilateral, &c. 



This little species, which is of thickish substance for a shell living in such deep 

 water, was obtained at a depth of more than 1000 fathoms in excess of that reached 

 by any other Leda obtained bv the Challenger. 



