428 



BASILISSA. 



longitudinal ribs ; farther in its walls are marked by hair-like lines 

 of growth and faint spirals. 



Alt. '12 in., diam. '14, least '11 ; penultimate whorl, '23. Mouth, 

 height '063, breadth '061 inches. (Watson.) 



This species slightly resembles in sculpture the young of Mar- 

 garita striata, Brod. (Trochus cinereus. Couth., nee Da Costa), 

 but in all details of form and ornamentation is very different. 

 From Trochus amabilis Jeffr., besides the generic features, it differs 

 in the depressed spire, in the absence of the deep-cut suture, in the 

 flatness of the base, and in all the features of minute sculpture. 

 From Basilissa reticulata (Solarium), Phil., it differs in being much 

 rounder on the base, blunter at the edge of umbilicus and at the 

 carina, and in being much less delicately sculptured. ( IPafeon.) 



Gulf of Mexico, 15-640 fms. 



B. costulata WATSON, Jour. Linn. Soc. Lond. xiv, p. 600 ; Chal- 

 lenger Gasterop., p. 103, t. 7, f. 11. DALL, Bull. M. C. Z. ix, p. 48, 

 1881. B. (Ancistroba*is) costulata Wats., var. depressa DALL, 

 4 Blake ' Gasterop., p. 384, t. 23, f. 4, 4a. 



Var. DEPRESSA Dall. PI. 60, figs. 14, 15. 



The shell figured differs from B. costulata, as described and 

 figured by Watson, in the less flexuous radiating costse, which are 

 nearly equal to the interspaces in width, and in the smaller number 

 of spiral ridges, which are about ten on the base and seven to nine 

 on the upper surface of the whorls. The armature of the mouth is 

 a character which does not appear until full maturity, so that I do 

 not regard its non-existence in the Challenger specimens as im- 

 portant. The other characters seem to agree closely with Watson's 

 figure and description, and, taking into consideration the known 

 variability of the abyssal shells and among the Blake specimens of 

 this species, I do not feel justified in separating the Blake shells 

 specifically from B. costulata. If I am correct in the identification, 

 this material enables me to add a good deal to the knowledge of 

 the species and genus. The dried remains of the animal in one 

 specimen bear a pellucid multispiral operculum a little more cir- 

 cular in outline than that of Seguenzia, but otherwise precisely 

 like it. 



The aperture in the adult is strongly thickened a little distance 

 within its margin, which remains sharp. The projecting peripheral 

 part is a little bent in, recalling the aperture of Seguenzia. The 



