MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 425 



is long, narrow, and oblique. H. (?). B. 012S. Mouth, 

 height 0-14, breadth 0'039. Penultimate whorl, height O078. 



27. Pleurotoma (Drillia) incilis, n. sp. 



St. 24. March 25, 1873. Lat. 18° 38' 30" K, long. 

 65° 5' 30" W. N. of Culebra, island of St. Thomas, Dan. W. 

 Indies. 390 fms. Coral-mud. 



Shell. — Fusiform, narrow, finely ribbed and spiralled, with a 

 high, conical, subscalar, fine-pointed spire ; a short conical base 

 produced into a small, narrow, triangular snout. Sculpture. 

 There are fine sharpish riblets parted by furrows of twice their 

 breadth, which run pretty continuously with a slight dextral 

 twist from whorl to whorl ; there are about eighteen or twenty on 

 the last whorl, and fewer on each preceding whorl ; they are a 

 little oblique, and on the base sinuous ; they originate below the 

 sinus-area and run down to the inferior suture ; on the base they 

 become finer and more crowded, and gradually die out without 

 reaching the snout ; the lines of growth are shown by fine close- 

 set scratches. Spirals — immediately below the suture there is a 

 broadish depressed band constituting the sinus-area, only marked 

 by the lines of growth ; this band at the top of each whorl gives 

 the scalar appearance to the spire : below this is a slight raised 

 border, where the longitudinal ribs arise ; and here there is an 

 angulation of the whorl, which is sharp and median on the upper 

 whorls, but is less so on the last. Close below the border of the 

 sinus-area is the first spiral thread, a series of which, fine, rounded, 

 little raised, cover the rest of the shell, rising into small knots on 

 the riblets ; of these threads there about two on the earlier whorls, 

 four on the penultimate, and about nine or ten on the last, exclu- 

 sive of those on the snout, of which there are about nine ; of these 

 the highest are a little stronger, and the following ones a little 

 more crowded than the others. The whole surface of the shell is 

 microscopically granulated. Colour dead white. Spire high, 

 narrow, conical, subscalar. Apex consists of four conical embryo- 

 nic whorls rising to a minute rounded point a little bent over to 

 one side ; they have a sharp expressed keel and a broad, slightly 

 impressed suture. Whorls 11, rather short, of very regular 

 increase ; they have a sloping, slightly sunken shoulder, below 

 which they have a slight angulation, which is made prominent 

 by the swelling of the riblets and the spiral thread which con- 

 nects these ; from this point, which lies rather above the middle, 



