600 BEV. B. BOOa WATSON ON THE 



The form of this shell connects it with BasiUssa aUa, B. sim- 

 plex, and B. munda, and it distinctly has the sinuses of the 

 genus : the layer of nacre is very faint ; there is, however, a gleam 

 of it through the surface-layer, and within the mouth, in a favour- 

 able light and protected from light coming through the shell, 

 there is a distinct pearly lustre. 



It has some resemblance to JSufrochus gemmatus, Reeve, in form 

 and in its gemmed umbilicus ; and, though much higher and more 

 conical, recalls the Solaria of the group Torinia (Gray), especially 

 S. frochoides, Desh, 



6. Basilissa costulata, W.- 

 St. 24. Mar. 25, 1873. Off Culebra Island, St. Thomas, 

 Danish West Indies. 390 fms. Mud. Three rather young spe- 

 cimens. 



Shell. — Small, depressedly conoidal, sharply angulated, flattish on 

 the base, sharply and deeply umbilicated, a little porcellanous, 

 flexuously ribbed. Sculpture. The whole surface is covered with 

 longitudinal llexuous ribs, which are narrow, sharp, and uniform, 

 and each is about 0'002 in. broad, and they are parted by intervals, 

 which at the suture are twice and at the periphery thrice as broad 

 as the ribs. There are about 40 of these on the last whorl. They 

 are crossed by spirals, half the breadth of the ribs, running across 

 the intercostal spaces and forming knobs on the ribs. Of these 

 on the last whorl there are about seventeen, much closer-set 

 and less uniform than the ribs ; in particular the carinal spiral, 

 which is very sharp, and the fourth and seventh above it, are 

 stronger than the others ; the last mentioned of these is espe- 

 cially so on the earliest whorls. On the base the longitudinals, 

 though continued even into the umbilicus, become much less 

 prominent and are no longer nodose ; and the spirals, of which 

 there are about fifteen, are closer-set, broader and flatter, except 

 the first three below the carina, which are sharp and narron^. 

 The whole base is pit-marked from the spiral interstitial fur- 

 rows being cut up by the longitudinals. Colour dead white (on 

 the base a little glossy) on the thin porcellanous surface, through 

 which the nacreous layer behind gleams. Spire raised, with a 

 very slightly concave outline. Apex, which consists of the mi- 

 nute smooth embryonic whorl and a half, is itself a little flat- 

 tened, but rises sharply above the sculptured sui'face of the suc- 

 ceeding whorls. Whorls 5|, of slow and regular increase till 

 the last, which begins to enlarge rapidly. They are slightly 



