MUSEUM OF COMPARATIVE ZOOLOGY. 365 



Calliostoma tiara Watson. 



Calliostoma tiara Watson, Dall, Bull. M. C. Z., IX. p. 45, 1881. 



Trochus (Zizyphinus) tiara Watson, Lin. Soc. Journ., XIV. p. 696, Sept., 1879; 

 Chall. Gastr., p. 60, pi. vi. fig. 4, 1885. 



Habitat. Station 44, 539 fms. Station 2, 220 fms. St. Thomas and Ber- 

 muda, Watson, Challenger Expedition. 



Some specimens, especially those from off Havana, in 450 fms., which I 

 referred to this species in my Preliminary Report, I am now convinced are 

 distinct, and they are so described here under the name of ft corbis. The nu- 

 cleus of C. tiara is globular, and immersed to a greater or less extent. It looks 

 as if it was originally sinistral. 



Calliostoma corbis n. s. 



Plate XXXIII. Fig. 1. 



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 pe- 

 riphery, 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, reticu- 

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

 ing 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 overhangs 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 middle of it. Umbilicus none ; whorls flattened above between 

 periphery and suture; base rather rounded. Alt. 5.0, max. diam. 3.75 mm. 



Habitat, Off Havana, in 450 fms., Sigsbee. Station 20, in 220 fms. (with 

 ft tiara Watson). 



This species was at first confused with ft tiara Watson, which has not the 

 continuous strong network, and in which the nodules which represent the 

 intersections are of an imbricated character. The strong carina in ft corbis 

 forms the periphery, in ft tiara the homologous spiral is comparatively faint 

 and a little above the periphery. In ft tiara also the centre of the base is 

 indented, almost umbilicated, which is not the case in ft corbis. The latter is 

 a more solid shell, and the curious callosity on the pillar does not occur in any 

 of the specimens of ft tiara I have seen. 



