EEPORT ON THE LAMELLIBRANCHIATA. 313 



obsoletas pulcherrimc squamatis. Umbones parvi, acuti, Isevigati ; auriculae paulo 

 insequalos, postico majori, incrementi lineis lamellatis radiisque obsoletis divergcntibus 

 instructi. Lirse interuaj undecim gracillimse, extremitatibus parum incrassatis. 



This species, of which only a few right valves are at present known, is a little convex, 

 equilateral, rounded, but rather longer from the hinge to the ventral margin than across 

 from side to side. It is very thin, whitish, and slightly pellucid. The right valve is 

 sculptured with numerous very fine concentric laminae, which are altogether wanting on 

 the acute glossy beak, and towards the lower margin, in some instances, become rather 

 more crowded than elsewhere. They have an undulating character through crossing 

 slightly elevated radiating ridges. These vary in number according to the size of the 

 specimen, being about fifteen in small valves, and twice that number in the largest under 

 examination, every alternate ridge extending only about half-way from the circumference 

 to the umbo. Upon these rays the concentric lamellse, when not worn, are elevated into 

 vaulted scales, giving a very pretty appearance to the shell. The ears are small, somewhat 

 unequal, the front one being rather the larger. They are ornamented with the termina- 

 tions of the concentric laminae, which pass over two or three obsolete rays, more noticeable 

 on the posterior than the anterior side. The acuteness of the beak is somewhat variable, the 

 apical angle of divergence being 100 to 113 degrees. The internal surface is glossy, and 

 strengthened usually with eleven radiating lirse, but at times here and there an interven- 

 ing short one is met with. They are very slender, thread-like, scarcely thickened at the 

 extremities (excepting two or three of the uppermost), and gradually disappear as they 

 approach the umbonal region. 



Length 12 mm., height 13, probable diameter 3. 



Habitat. — Station 24, off Culebra Island, West Indies, at a depth of 390 fathoms ; 

 also Station 33, off Bermuda, in 435 fathoms. 



■Amussium obliquum, n. sp. (PI. XXIIl. figs. G-Ga). 



Testa compressa, tenuissima, semipellueida, umbones versus nitens, obliqua, irregu- 

 lariter rotundata. Valva sinistra in^quilateralis, liris coneentricis tenuissimis instructa. 

 Auriculae valde insequales, postica longe majori, superne acute angulata, inferne ab valva 

 sulco angusta profundo sejuncta. Umbo mediocriter acutus, latere obliquo postico 

 longiore. Lirse radiantes internae circiter sedecim, quarum paucae superiores crassiores 

 videntur. 



As but a single minute and probably young left valve is all that is at present known 

 of this species, it is with considerable hesitation that I have ventured to describe and 

 impose a name ujDon it. 



(ZOOL. CHALL. EXP. PART XXXV.— -1885.) JIlll 40 



