MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 91 



In many respects this species is very like T. zonatus, Wood 

 (= T. menkeanus, Phil.), but than that species this is much smaller 

 and higher ; the last whorl, which is the sixth in both, is here 

 much smaller and narrower, and the umbilicus is not covered by 

 the broad semicircular plate which characterizes that species. In 

 that, too, the coloured bands above are fewer and are very unequal, 

 and there are three of these on the base. T. (G.) fulgens, Gould, 

 is not unlike, but is higher, and the spirals are more numerous 

 and smaller. 



18. Trochus (Ziziphinus) arruensis, n. sp. 

 Sept. 18, 1874. Arru Islands, S. W. of Papua. 

 Shell. — Conical, carinated, with a flattened base, strong, opaque, 

 covered with tubercles, and coloured with grey and pink. 

 Sculpture. There are eight spiral rows of small round tubercles 

 on each whorl. The tubercles on the first two rows are larger 

 than the others ; these, as well as the next three rows, are parted 

 by distinct depressions ; the lowest three rows are much closer to- 

 gether, but project a little, especially the centre and largest row 

 of the three. On the base there are about nine less strongly 

 tubercled spiral threads, with feebler threads between, these in- 

 termediate threads becoming feebler towards the centre. The 

 tubercles are smooth and polished, but the whole intervening sur- 

 face is sharply fretted with fine oblique puckerings. Colour 

 white, beautifully flecked above with greyish-purple blotches, and 

 closely spotted with purplish pink on the base. Spire high and sharp- 

 pointed, its concavely conical slope being slightly broken at the 

 sutures by the projection of the two superior rows of tubercles. 

 Whorls about 10, flat and of very regular increase. Suture slight, 

 but distinct, being defined by the slight carinal spiral above, and 

 the double row of larger tubercles below. Mouth rather small, 

 square and very oblique. Outer lip sharp but strong. Inner lip 

 strengthened internally by a buttress of porcellanous nacre, which 

 ends abruptly towards the point of the pillar, forming a tooth. The 

 pillar, bevelled off to a sharp edge, is pressed back on the umbilicus, 

 which it completely closes, leaving only a central depression and 

 a postcolumellar furrow. Operculum thin, yellow, normal. H. 

 0-64. B. 0-58, least 052. Penultimate whorl 018. Mouth, 

 height 0'42, breadth 03. 



This species very much resembles T. decoratus > Phil., but that 

 species is more highly narrowly conical, is flatter on the base, and the 

 whole system of spirals is different. In T. decoratus also the earlier 



