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



It is compressed, very thin, semitransparent, of an oblique growth, so that the 

 hinder side is larger than the anterior. It is sculptured with very slender concentric 

 lirse, which become mere striae towards the glossy umbo. This is moderately acute, 

 the converging sides, of which the posterior is considerably the longer, meeting at 

 an angle of about 122 degrees. The ears are very unequal, the hinder one being 

 decidedly larger, denticulate along the top, and separated beneath from the umbonal 

 slope by a narrow deep groove above, parallel with which is an elevated ridge 

 bordering the auricle. It is acutely angled above and cuts in deeply below. The 

 interior is strengthened with sixteen radiating ridges, the two uppermost (of which that 

 on the posterior side is almost obsolete) forming the base of the ears. One or two of the 

 upper ones on each side are very short, and appear thicker than the rest, although in 

 reality they are not. None extend to the beak, so it is probable that very young shells 

 are destitute of lirse. 



Length 3 mm., height 2f. 



Hahitat. — Station 24, off Culebra Island, West Indies, in 390 fathoms; Pteropod ooze. 



This minute valve, although without doubt very young, indicates a species of a 

 peculiar oblique growth distinct from any as yet known. 



Amussium propinqimm, n. sp. (PI. XXIII. figs. 7-76). 



Testa valde compressa, tenuissima, pellucida, nitida, rotundata ; valva dextra laevis, 

 incrementi lineis parum conspicuis sculpta, sinistra radiatim tenuiter lirata. Auriculae 

 subsequales, lateribus concavis. Pagina interna nitida, luis capilliformibus duodenis 

 instructa. 



This species, of which only two odd valves are at present known, is very fragile, 

 pellucid, much flattened, glossy, and about ecjuilateral. It is of a rounded form, perhaps 

 a trifle longer than high, and has rather a long hinge-line. The auricles are small, not 

 quite equal, those of the right valve (the only one perfect at this part) being decidedly 

 concave at the sides, and sculptured with fine lines of growth. The umbones are small, 

 project a trifle beyond the straight hinge-margin, and have the sides very faintly concave 

 and converging to an apical angle of about 125 degrees. The right valve is smooth, 

 exhibiting only very fine lines of increase, which, however, are rather more visible near the 

 outer margin than elsewhere. The left valve, besides these concentric striae, is sculptured 

 with numerous fine radiating lirse. The interior of the valves is glossy, and strengthened 

 with twelve excessively fine hair-like lirse, which attain neither to the umbones nor 

 to the circumference. The shorter ones beneath the ears are the thickest. The left 

 valve appears radiately striated within, each stria corresponding with an external lira. 

 The ligamental pit is very minute. 



