REPORT ON THE GASTEROPODA. 665 



Shell. — Narrowly cylindrical, truncated in front like Cylichna alba (Brown), smooth, 

 thin, polished, with a small disk-like minutely perforated top. Sculpture: Longitu- 

 dinals — there are very faint and slight lines of growth. Spirals — there are some very 

 doubtful indications of a coarse spiral structure in the texture of the shell. Colour milky 

 white and glossy. Mouth the full length of the shell but not more, extremely narrow 

 with lips nearly parallel till they diverge in front, the inner lip following the slow basal 

 contraction, while the outer expands a very little, as is the case in Cylichna umbilicata 

 (Mont.) ; at the upper end is a small, narrow, but deepish rounded sinus. Outer lip : its 

 edge is very straight, retreating a little quickly above and slightly in front ; its direction 

 is straight, with the very slight bend to the right spoken of 'above. Top a little con- 

 tracted, rounded, with a sort of thickened pellucid disk 1 which is almost perfectly 

 horizontal, so that the whole top of the body-whorl and the upper corner of the mouth 

 are on the same level : in the centre is a minute closed pore. Inner lip : there is a thin 

 narrow glaze which thickens and expands in front : it is not expanded on the top. Pillar- 

 is short, slightly oblique and twisted, with a strongish defined tooth, in front of which it 

 is rather abruptly truncate. H. 0'156 in. B. 0'066. Mouth, breadth at same place, 0"014. 



Cylichna protracta (Gerald), is very like this in front, but rises much higher above. Cylichna 

 cylindracca (Pennant), is slightly slimmer or narrower in proportion to length, has the body-whorl a 

 little smaller, and the mouth slightly broader, lacks the slight posterior narrowing, and is squarely 

 truncate behind, while here the shell is rounded. The Challenger species, too, quite wants the very 

 peculiar form of the upper corner of the mouth which is characteristic of Cylichna cylindracca. 

 Cylichna alba (Brown), of the same size, is rounder and less cylindrical, being more attenuated above 

 especially ; the mouth is extended above the top of the shell ; the top of the body- whorl is more 

 oblique and less truncated. 



7. Cylichna tahitiensis, Watson (PI. XLIX. fig. 11). 



Cylichna tahitensis, Watson, Prelim. Report, pt. 19, Journ. Linn. Soc. Lond., vol. xvii. p. 320. 



September 28, 1875. Tahiti Harbour, near the reefs. 20 fathoms. 



Shell. — Cylindrical, thin, glassy, spirally striate from end to end, with a small body, 

 rounded outlines, no depression nor central point at the apex, and a toothless but abruptly 

 truncated and prominent pointed pillar. Sculpture: Longitudinals — there are scarcely 

 perceptible lines of growth. Spirals — the whole surface is covered with fine grooves not 

 quite regular, about -^j inch apart, but weaker and more crow T ded in the middle than at 

 either extremity. Colour bluish transparent glossy white. Mouth rather large and long. 

 Outer lip has a sinus just above the body, rises and is angulated at the outer upper corner 

 of the shell : from this point its edge advances and its line is slightly convex, tending in 



1 Hence its name. 



(ZOOL. CHALL. EXP. — PART XLII. 1886.) Tt 84 



