604< ON THE MOLLUSCA OP THE ' CHALLENGER ' EXPEDITION. 



long. 139^ 28' E. 345 fms. Sandy mud. 1 specimen, not quite 

 full-grown. 



Shell. — Higli,concavely conical, carinated, sculptured on the upper 

 whorls, smooth or wrinkled below, thin, with a tumid lirated 

 base, narrowly umbilicated, with a smooth epidermis, thin, 

 but especially so on the base. More or less nacreous all 

 over under a thin porcellanous upper layer. Sculpture. The 

 first three whorls (after the embryonic apex) are reticulated 

 by three sharp remote spirals, and rather stronger, slightly 

 oblique longitudinals, which rise at their intersection into 

 small sharp pyramidal tubercles ; the interstices are a little 

 broader than high. This system gradually dies out and leaves 

 the surface smooth, only the row of infrasutural tubercles sur- 

 vives in an enlarged but depressed form, and springing from 

 these some sinuous oblique and slightly irregular longitudinal 

 puckerings appear on the last whorl, which is nearly bisected 

 by the sharpish, slightly expressed, finely tubercled carina. 

 This bisection of the last whorl arises from the great prolonga- 

 tion and tumidity of the base, on which, below the carina, are 

 five narrow^ equally parted, spiral threads, and two intraum- 

 bilical ones, w^hich are more contiguous. Besides this larger 

 system of sculpture, the whole surface is covered with minute, 

 oblique, irregular, and interrupted puckerings of the epidermis. 

 Colour a brownish yellowy but below the epidermis there is 

 a thin pure white porcellanous layer, through which and the 

 epidermis th*e sheen of the nacreous layer gleams. The base 

 is whiter, the epidermis there being very thin. Inside the 

 mouth is an exquisite roseate nacre. Spire high, with a slightly 

 concave contour, the lines of which are hardly swollen out by 

 the slight tumidity of the last whorl. Apex eroded, but evi- 

 dently small. Whorls 7 or 8, of regular increase, quite flat, 

 except the last, which is very slightly constricted below the 

 suture, a very little tumid on the upper slope, sharply cari- 

 nated but not much angulated at the suture, and very tumid 

 on the base. Suture linear, strongly defined above by the 

 square furrow lying between the lines of tubercles which margi- 

 nate the suture above and below. On the last whorl it be- 

 comes slightly pouting, from the projection of the carina and 

 the slight infrasutural constriction. Mouth nearly square, very 

 little oblique in the line of its advance, but standing out a little 

 obliquely to the axis of the shell. Outer lip thin, not descend- 

 ing. Pillar-lip thin, spread out broadly at its base over the 



