96 THE VOYAGE OF H.M.S. CHALLENGER 



epidermis there is a thin pure white porcellanous layer, through which and the epidermis 

 the sheen of the nacreous layer gleams. The base is whiter, the epidermis there being 

 very thin. Inside the mouth is an exquisite roseate nacre. Spire high, with a slightly 

 concave contour, the lines of which are hardly swollen out by the slight tumidity of the 

 last whorl. Apex eroded, but evidently small. Whorls 7 or 8, of regular increase, quite 

 flat on the side slopes, except the last, which is very slightly constricted below the suture, 

 a very little tumid on the upper slope, sharply carinated but not much angulated at the 

 suture, and very tumid on the base. Suture linear, strongly defined on the upper whorls 

 by the square furrow lying between the lines of tubercules which marginate the suture 

 above and below. On the last whorl it becomes slightly pouting, from the projection of 

 the carina and the slight infra-sutural constriction. Mouth nearly square, very little 

 oblique in the line of its advance, but standing out a little obliquely to the axis of the 

 shell. Outer Up thin, not descending. Pillar-Up thin, spread out broadly at its base 

 over the umbilicus, which it largely conceals, with a deep narrow furrow behind it. 

 Curving over to the right, it advances, thin and pointed, to its angular junction with the 

 basal lip. Umbilicus defined by a spiral thread and with two other spirals within it. It 

 is not small, but is concealed by the pillar-lip. H. 0*82 in. B. 0'63, least 0"53. Penul- 

 timate whorl, 0-19. Mouth 0'4 ; breadth 0'38. 



Trochus (Cantharidiis) iris, Humph., while totally unlike in most respects, slightly approaches 

 this in form. It is evidently not remote from Trochus argenteonitens, Lischke (Japan. Meeres Conch, 

 vol. hi. p. 67), a species I know only from the figure and description. The whole sculpture, how- 

 ever, seems distinct though similar. 



4. Basilissa, 1 Watson, 1878. 

 Basilissa, Watson, Prelim. Keport, pt. 3, Journ. Linn. Soc. Lond., vol. xiv. p. 593. 



Shell conical, carinated, umbilicated, nacreous : the last whorl is sinuated above : the 

 pillar is straight and in its direction but little oblique, thin, hollowed out above, in front 

 hardly toothed, but at the base strongly angulated : the mouth is rhomboidal : the outer 

 and the inner lip do not approach one another, nor are united by any palatal callus. 



The special feature of this genus is the sinus in the outer lip near its insertion. In the 

 presence of such a sinus it resembles Seguenzia, Jeffr., but differs from that genus in this, that 

 Basilissa has a wide, open, shallow, not a deep-cleft sinus ; is brilliantly nacreous, and lacks the 

 sharp tooth on the pillar, with the strongly marked sinus above and below it. It also wants the 

 carinal sinus which all the species of Seguenzia I have examined present ; and the basal sinus can 

 scarcely be said to exist, though on the base the lines of growth change their direction markedly 

 below the carina. 



In form, in sculpture, and in its sinus this genus recalls Platyschisma, M'Coy, a Carboni- 

 ferous fossil ; but that belongs to the Solariidas, and is distinguishable at once by the absence of the 



1 fiaalXitsaa, queen. 



