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



Lunula augustissima, elongata, vix impi-essa, angulo levi circumscripta, prope medium 

 promiueus. Area latior, profundior, striata, in medio linea impressa arcuata notata. 

 •Dentes ad 34, acuti, erecti. 



This species is of an elongate-oval form, but produced to an acute point behind. It 

 is about equal-sided, not particularly convex, white and glossy. The valves are of 

 moderately strong texture, exhibit a slightly curved keel behind, defining the dorsal 

 area, and are sculptured with fine concentric striae, which are rather deeper towards the 

 carina than on the anterior side, and are more or less interrupted for a small space a 

 little in front of the middle, the surface, in consequence, at this part being conspicuously 

 smooth and glossy. The striae just in front of the keel ascend somewhat suddenly, and 

 appeal- a little irregular owing to a very faint depression at this point. The dorsal 

 margins are about equally sloping, the front one being a little convex, the posterior 

 a trifle excavated at first, then prominent, and again concave at the end. The lunule 

 is very narrow, defined by a slight ridge, striated and slightly impressed. The area is 

 much broader, strongly striated, deep at the surrounding keels, prominent along the 

 middle, and exhibits on each side of it a second fainter ridge, enclosing a space about 

 the size of the lunule. The teeth are sharp, erect, and about thirty to thirty -four in 

 number, of which a small majority are in front of the small triangular ligament-pit. 



Length 7 mm., height 4, diameter 3. 



Habitat. — Station 188, south of New Guinea, in 28 fathoms; green mud. 



This species is a more finely sculptured shell than Leda ventricosa, Hinds, not so 

 acuminate behind, and is jjeculiar on account of the cessation of the striae near the 

 middle of the valves. 



Leda watsoni, n. sp. (PI. XIX. figs. 11— 11«). 



Testa jiarva, alba, subfecjuilateralis, ovata, antice acute rotundata, jjostice acuminata 

 et bicarinata, inter carinas concava, concentrice lirata, liris tenuibus, fere aequalibus, 

 interstitiis gracdioribus, ad impressionem flexuosis. Margo dorsi anticus paulo declivis', 

 leviterque excurvatus, posticus longior, fere rectilinearis, aeque obliquus ; margo inferior 

 late arcuatus, pone carinam anticam aliquanto emarginatus. Lunula augustissima, 

 linearis ; area postica latior, lanceolata, impressa, in medio promineus, prope medium 

 linea elevata paulo arcuata utrinque instructa. Dentes ad 24, mediocriter validi. 



This species is of an elongate, trigonally ovate form, sharply rounded in front, and 

 terminating behind in an acute point. It is white, glossy, moderately convex, and 

 almost equilateral, the posterior side being only very slightly longer than the anterior. 

 The valves exhibit two distinct and slightly arcuate keels at the hinder end, one 

 running from the beaks to the acute extremity, and the other a little below it, the 

 space between being conspicuously concave. The sculpture consists of fine, regulai-, 



