MOLLUSCA OP THE ' CHALLENGED ' EXPEDITION. 107 



of slow increase and straight outline, with about one varix on 

 each. Suture a very little impressed at the base of each whorl. 

 Mouth oval, with a sharp angulation at the canal aud at the upper 

 corner, where the lip is sinuated and piuched in against the body- 

 whorl, and where the corner is further narrowed into a little 

 canal by the strong tooth which rises nearly on the interior basal 

 thread. Outer lip sharp, fluted on the edge, thickened by an ex- 

 ternal varix ; ascending a little at its junction with the body-whorl, 

 it retreats so as to form a slight sinus ; it sweeps round with a very 

 equable curve, advancing about the middle into a patulous wing- 

 like projection ; across the base it is flat, advancing, but scarcely 

 patulous. The anterior canal is rather narrow and deep, short, 

 bent back, and with its front margin reverted all round except 

 on the pillar. Pillar short, angulated, and slightly twisted in 

 front where it bends to the left, sharp-pointed. Inner lip thick- 

 ened, and forming a ledge along its whole length. H. 0"8. 

 B. 0-27, least 0-22. Penultimate whorl 012. Mouth, length 

 0-2, breadth 0-17. 



7. Cerithium (Bitthtm) lissum, n. sp. (Xissos, smooth.) 



July 29, 1874. Levuka, Fiji. 12 fms. 



Shell. — Conical, rather stumpy, a little contracted and drawn out 

 on the base, longitudinally ribbed, smoothed, of a brownish-white 

 colour. Sculpture. Longitudinals — towards the apex there are 

 on each whorl about twelve small, rounded, rather hunchy, 

 straight and regular ribs, parted by hollows broader than the 

 ribs ; these very soon become less regular, and, though larger, 

 are less so relatively to the size of the whorls and to the breadth 

 of the hollows between them. On the penultimate whorl they 

 become nodose, especially on the lower part of the whorl, and on 

 the last whorl they are almost entirely replaced by unconnected 

 rows of tubercles. The surface is very faintly scratched with lines 

 of growth. In the middle of the last whorl there is a pretty strong 

 white varix, broad above and projecting below. Spirals — there 

 are many (on penultimate whorl about 20) irregular, unequal and 

 unequally-parted scratches, three or four of which are markedly 

 larger than the rest. Baised between these h'e minute hair-like 

 lines, with here and there a flat thread, which, in crossing the 

 ribs, rise, at the top and especially near the bottom of the whorls, 

 into rounded tubercles. On the last whorl there are four rows 

 of these tubercles — one just below the suture, where they are 



8* 



