MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 465 



Whorls 5, below the embryonic apex ; probably about 9 in all. 

 The rows of infrasutural tubercles give them a minute double 

 keel above with an oblique slope at this part, below which they 

 are cylindrical, or very slightly contracted to the lower whorl : 

 this contraction is distinct on the last whorl, which is very small. 

 The base is rounded and contracted, and ends bluntly in a trian- 

 gular snout with a slightly reverted point ; the advance of the 

 pillar on the left side is rather more than one would have ex- 

 pected. Suture small, but very strongly marked. Mouth ovate, 

 contracted and angulated above, produced into the broad, open, 

 and oblique canal below. Outer Up confused by having been 

 broken and mended; but apparently thickened and probably mar- 

 gin ated above, very flatly curved with great regularity from end 

 to end ; the edge runs very straight with little of prominence, 

 and forms a very slight and shallow rounded sinus near, but not 

 quite close to, the suture, from which it seems to be separated 

 by an extension of' the upper beaded line. Inner lip broad, 

 formed by a glossy pad above, and below it is slightly excavated into 

 the substance of the shell. It runs straight out along the pillar 

 to the very point, where it meets the very oblique, twisted, and 

 thickened edge : the pillar is thus very short, stumpy, and obliquely 

 cut off in front, reminding one of a Nassa ; and its whole point is 

 a little twisted and reverted. H. 0'31. B. 013. Penultimate 

 whorl, height 006. Mouth, height 0-13, breadth 0-07. 



57. Pletjbotoma (Deerancia) ctrcttmvoluta, n. sp. 



St. 23. March 25, 1873. Lat, 18° 38' 30" K, long. 65° 5' 30" W. 

 North of Culebra Island, St. Thomas, Danish West Indies. 

 390 fms. Coral-mud. 



Shell. — "White, strong, with a high, scalar, small, buff-tipped 

 spire, an excessively small body, and a contracted conical base. 

 Sculpture. Longitudinals — there are on each whorl about 14 slight, 

 narrow, ridge-shaped, round-topped, oblique and slightly irre- 

 gular riblets ; they rise sharply in obscure tubercles below the 

 sinus-area, and die out at the point of the base ; they are parted 

 by shallow rounded furrows of more than twice their breadth. 

 The sinus-area is scored by minute cusp-like remote bars, which 

 generally are not continuous, but are interrupted about the 

 middle, and are more numerous on the lower than the upper half 

 of the area : the lines of growth are extremely fine. Spirals' — 



