MUSEUM OF COMPARATIVE ZOOLOGY. 323 



a stronj^ rounded elevated thread under wliich the anterior ends of the trans- 

 verse cosla' appear to be inserted, f'ornun;^' pits between tlieni and rendering' the 

 outline of the l)asal surface somewhat stellate; witliin the margin there are one 

 or two strong and iiunierous fine spiral thrc^ads, Imt the transverse sculpture 

 seems obsolete; the aperture is rounded to the right, slightly flattened on the 

 basal side, and narrowed behind; inside white and polished and with a slightly 

 projecting margin behind which is the broad face of the thickened varix, over 

 wliirh the sculpture of the whorl is continued to meet the aforesaid margin; 

 the aperture is entire, but the axis is imperforate and the whorls closely adja- 

 cent; the operculum is pale translucent yellow, of about three turns. Lon. of 

 shell, 11.0; of last whorl, 3.6; of aperture, 1.5; max. lat. of last whorl, 2.75; 

 of the basal area, 1.5 mm. 



Habitat. Station 200, off Martinique, in 270 fms., fine sand and mud, bot- 

 tom temperature 49°. F. 



This beautiful little species has quite a different aspect from the S. crenulata 

 group, to which it is most nearly allied. The yellowish color, which was quite 

 marked when fresh, has in a year faded considerably, though the shell has not 

 been exposed to the light. The operculum differs from that of the northern 

 and extreme southern Opalioe in being thin, yellow, and translucent, instead of 

 opaque and black. 



Scala (Opalia) concava n. s. 



Shell dead and brown, with the nucleus and basal whorl imperfect; the color 

 is probably grayish or brownish white when in good condition; whorls 12-14, 

 excluding the nuclear whorls; transverse sculpture of about eleven strong, nar- 

 row, elevated, round-topped ribs extending across the whorls, which last, in the 

 young stages, are somewhat rounded, but near maturity are quite flattened; 

 the ribs are not continuous nor exactly alternate from whorl to whorl, but fall 

 in with some irregularity; beside the ribs there are many close, fine, even, 

 slightly elevated threads covering the whole surface and corresponding appar- 

 ently to the incremental lines; longitudinal sculpture consisting of similar but 

 less uniform revolving threads which cover the whole surface, but which a 

 short distance before the suture are for a little space more distant, coarser, and 

 more prominent than elsewhere; the intersection of these with the transverse 

 threads gives the surface a decayed or porous appearance under strong magni- 

 fication; beside this there is a single strong not much elevated carinal rib 

 which revolves at the periphery of the base, and between the whorls forms a 

 cord-like ridge separating the transverse ribs on one whorl from the same on 

 the next wdiorl; the anterior margin of the suture is appressed toward this 

 carina very closely; the base of the shell is smooth, and in the type quite con- 

 cave from the carina to the pillar, but in the last adult whorl when perfect it 

 is probably nearly flat; aperture rather small, angulated by the end of the 

 carina, squarish. Lon. of shell, 14.0; max. lat., 4.0 mm. 



Habitat. Sand Key, 15 fms., with Pagurus. 



