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



almost stands on the edge of the base. Pillar lip expanded on the base, bat with an 

 abruptly defined edge, blunt but projecting on the pillar, where in front it is covered by 

 and cemented to the outer lip. H. - 22 in. B. - 07, least 0'06. Penultimate whorl, 

 height 0-032. Mouth, height 0-037, breadth 0-035. 



This beautiful little species is very like in general aspect to Triforis perversa (Linne) ; but, apart 

 from other obvious differences, the sculpture of the apex is quite distinct. In that species the 

 extreme apex has about seven spiral scratches, parted by roughened threads, and the following 

 whorls are beset with much closer-set and more numerous riblets, and they have two close-set spirals 

 at the carina; the whole of this sculptured apex, too, is stumpier, and the whorls are not so 

 angulated, and the extreme point is blunter. 



Triforis hindsii, Desh. (Bourbon Moll., p. 99), is very near, but is less contracted in front 

 towards the base, has not there near the mouth four rows of pearls, has the pearls white on a brown 

 ground, has not the single amber thread round the base of each whorl, and is a little narrower in 

 proportion. 



3. Triforis bigemma, Watson (PI. XLIII. fig. 6). 



Cerithium (Triforis) bigemma, Watson, Prelim. Report, pt. 5, Joura. Linn. Soc. Lond., vol. xv. p. 101, 



sp. 2. 

 Triforis bigemma, Dall, Moll. " Blake " Dredgings, Bull. Comp. Zool. Harvard Coll. Cambridge, 

 vol. vi. No. 3, p. 81. 



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

 Island, West Indies. 390 fathoms. Pteropod ooze. 



Habitat. — Yukatan Strait, 640 fathoms (Dall). 



Shell. — Sharply conical, high and narrow, solid, opaque, brilliant, yellowish white. 

 Sculpture : Longitudinals — the whorls are crossed by rows of tubercles with broad and 

 rounded hollows between; of these longitudinal rows there are 17 to 18 on the last, and 

 about 14 on a great many of the preceding whorls; besides these the surface is sharply, 

 distinctly, and pretty closely scored by minute lines of growth. Spirals — a prominent 

 spiral band encircles the whorls formed by two rows of rounded tubercles, which in each 

 row are connected by a spiral thread ; of these threads the lower is rather the larger, 

 sharper, and more prominent. The distance between these threads is very nearly the 

 same as that between the longitudinal rows, so that each group of four adjoining tubercles 

 forms nearly a rhomb. Pound the upper part of each whorl is an impressed flat surface, 

 in which, very near the suture, lies another smaller spiral, which becomes minutely 

 tubercled where it crosses the longitudinal rows. At the bottom of each whorl is a very 

 minute spiral thread, which forms a pouting edge to the suture. Besides these the surface 

 is faintly reticulated by microscopic spirals crossing the longitudinal lines of growth. 

 This reticulation is best seen on the flat and glossy base, which is unbroken except by a 

 small sharp spiral, about 0*012 in. within the edge. Colour yellowish white, pure white 



