REPORT ON THE LAMELLIBRANCHIATA. 309 



Length 48 mm., height 52, diametei' 8. 



Habitat. — Statiou 33, oft* Bermu(Li.s, in 435 i'uthoras ; coral mud. 

 This fine species is dedicated to Mr. W. H. Dall as a mark of high esteem on 

 account of his many and valuabh) papers on raahicology. 



Amussium watsoni, n. sp. (PL XXIL figs. 8-8c). 



Testa tenuissima, subdiaphana, alliiihi, paido inajquivalvis, sul)circularis, sericato- 

 nitens, utrinque conspicue hians. Valvte compressre, diverse sculptse. Valva dextra 

 profundior, paUidissime fuscescens, liris confertis eoncentricis prope marginem angus- 

 tissime himelLatis ornata, sinistra similiter lirata, sed etiam liris gracilibus radiantibus 

 umboncs vei'sus prsecipue cancellata. Auriculae parva3, increment! lineis aliisque 

 radiantibus instructse. Pagina interna nitida, marginem versus leviter iridescens, liris 

 albis radiantibus 10-12 baud ad marginem extensis munita. 



o 



This charming species is almost circular, very thin and fragile, considerably 

 gaping on both sides above the middle, a little inequivalve, the one valve which 

 I regard as the right being a trifle more swollen than the other. It is also a trifle 

 thinner and of a very light brownish tint. The left valve is of a milky white colour, 

 and consequently rather less transparent. The exterior of the valves is beautifully 

 glossy and has a silky appearance. Both are very finely, concentrically lirate, the 

 hrse towards the outer margin in the right valve being very narrowly lamellated. In 

 addition to this ornamentation the left valve exhibits numerous fine radiating liras, 

 which are decidedly elevated for a short distance around the um bones, and then 

 gradually, further out, take the form of faint substriations. The ears are of moderate 

 size, al)out equal on each side, and sculptured with elevated lines of growth and others 

 diverging from the beaks, the former sometimes forming a sort of serrate dorsal edge. 

 The umbones are moderately acute, with an angle of divergence of about 125 degrees. 

 The interior is glossy, somewhat iridescent around the margin, and strengthened with 

 from five to six pairs of white riblets of dilferent lengths, the longest becoming obsolete 

 at some distance from the circumference. 



Length 50 mm., height 52, diameter 9g. 



Habitat. — Station 218, north-east of New Guinea, at a depth of 1070 fathoms. 



This lovely species, one of the prizes of the Expedition, I feel much pleasure 

 in naming after my friend the Rev. R. P)00g Watson. 



Amus.num caducum, n. sp. (PL XXIII. figs. 1-lc). 



Testa tenuissima, pellucida, rotundata, compressa, superne angustata, producta, paulo 

 ina^quivalvis (valva dextra sinistra leviter convcxiore) utrinque cons])icue hians. Valva 



