60 THE VOYAGE OF H.M.S. CHALLENGER. 



space between this and the suture is divided pretty equally by two threads, the lower of 

 which is feeble. On the upper wborls all of these are closely beaded, on the last whorl 

 only the two highest are so. Below the carina is another remote strong thread, which 

 meets the outer lip ; within it is another, not quite so strong nor so distant, and occupying 

 the space from this to the middle are five flat close-set tbreads, followed by three rather 

 more separated and roughly beaded threads, the inmost of which, like a twisted cable, 

 forms a sort of pillar with a chink between it and the sharp edge of the pillar-lip, and 

 advances into a small tooth at the angle where it joins the outer lip on the base. Longi- 

 tudinals — the whole surface is roughened by rather coarse oblique lines of growth, which 

 on the upper whorls appear as oblique reticulating ribs. Colour white, with a translucent 

 calcareous layer over nacre. Spire rather high, scalar. Apex a little flattened down and 

 rounded, the minute rounded embryonic 1^ whorl scarcely rising above the level. Whorls 

 6, of rather rapid increase, with a narrow flat shelf below the suture, thence sloping flatly 

 to the shoulder-carina, from which point the contour-line descends perpendicularly; the 

 base is inflated at the edge and flattened in the middle. Suture deeply impressed between 

 the narrow flat shelf below and the overhanging carina above. Mouth slightly oblique, 

 but with a perpendicular pillar, round ; nacreous within. Outer lip thin, transparently 

 porcellanous on the edge, but thickened by nacre within. Pillar-lip perpendicular, rounded 

 within the mouth, advancing to a sharp point in front, slightly reverted but not appressed, 

 having a small open furrow and a minute umbilical chink behind it. H. 0"3 in. B. 0*26, 

 least 0-22. Penultimate whorl, 0-053. Mouth, height 0-14, breadth 014. 



This species extremely resembles Trochus occidentalis, Migh. (see PL VI., fig. 2 *), but is smaller, 



is broader in proportion, with a less high spire ; the apex is not sharp and projecting, but flattened 



down and rounded ; the whorls are much more scalar, and of more rapid increase ; the base is more 



on its outer tumid edge and more rounded. The apex is ornamented with a 



/ JH^ microscopic and quite irregular inlaid work of angular depressions, parted by 



>.,.. . WW very narrow interrupted raised lines ; whereas in that species the ornamentation 



Ornamentation of apex, is like honeycomb, with relatively large, nearly regular hexagonal pits and 



"talU. phorus raised flat borders. This difference is shown in the woodcut. The threads 



on the base are approximate, not parted in the middle by a smooth zone, and 



the pillar-lip is not appressed as in that species ; the outer lip, too, is thickened within by the layer 



of nacre. 



18. Trochus (Ziziphinus) tiara, 1 Watson (PI. VI. fig. 4). 



Trochus (Ziziphinus) tiara, Watson, Prelim. Report, pt. 4, Journ. Linn. Soc. Lond., vol. xiv. p. 696. 

 CaUiostoma tiara, Ball, " Blake " Dredgings, Bull Mus. Conrp. Zool., Cambridge, U.S.A., vol. vi. p. 45. 



Station 24. March 25, 1873. Lat. 18° 38' 30" N., long. 65° 5' 30" W. Off Culebra 

 Island, West Indies. 390 fathoms. Pteropod ooze. 



1 So called from its high narrow form. 



