CALLIOSTOMA. 381 



hind it. Umbilicus a small open depression leading into a minute 

 central pore. The slopes of the depression are obliquely scored by 

 the tubercles of the central basal thread. 

 Alt. G'22 in. ; diam. 0*16 inch. ( Watson.') 



Of Cidebra Island, West Indies, in 390 fms. 



Trochus (Ziziphinus) tiara WATSON Journ. Linn. Soc. London 

 xiv, p. 696; Challenger Gasterop., p. 60, t. 6, f. 4. Calliostoma 

 t id ru Watson, DALL, Bull. Mus. Comp Zool., vi, p. 45; 'Blake' 

 Gasterop., p. 365. 



This beautiful little shell offers some rather perplexing features ; 

 for the curves of growth on the base indicate a slight sinus toward 

 its outer edge, which, indeed, is shown in the actual mouth-edge, 

 a peculiarity suggestive of the genus Basilissa ; but there is not 

 seldom in the Trochidse a tendency to a backward curve of the lip- 

 edge at that point; and in this species there does not exist the 

 characteristic infra-sutural sinus which would connect it with 

 Basilissa or with Seguenzia, to which its tuberculated pillar and 

 closed umbilicus rather point. ^[<u</<lrita carinata A. Ad., from 

 the Philippines, has some points of resemblance with this, but is 

 obviously very differently marked in the form of the umbilicus. 

 ( 



C. CORBIS Ball. PL 48, fig. 7. 



Shell small, white, with a glassy minute apparently dextral nucleus 

 and about six whorls. The first one or two have concave arched 

 transverse ribs, and resemble a bit of a small Scala ; the others are 

 very strongly reticulately sculptured. The spiral sculpture consists 

 of one very strong rib on the periphery, a slightly weaker one near 

 the suture, and another (which is rarely absent) midway between 

 them ; on the base there are four strong spirals a little undercut at 

 their outer edges. Transverse sculpture of strong thin oblique radii 

 (27-30 on the last whorl) following the lines of growth, reticulating 

 the spirals (on crossing which they become slightly nodose) and 

 forming deep squarish pits, which are elongated in the adult by the 

 crowding of the radii toward the mouth. The suture appears 

 channelled, as the whorl falls short of the peripheral rib which over- 

 hangs it, but is not really so. The base is flexuously radiately 

 ridged but not reticulate; the aperture rounded, thickened within, 

 lirate ; the pillar thick with an obtuse knob (almost a tooth) about the 



