86 THE VOYAGE OF a M.S. CHALLENGER. 



The presence of this species at two such separate localities as Bermudas and Marion Island, 

 between the Cape and Australia, is interesting. 



51. Trochus (Margarita) illotus, 1 n. sp. (PJ. XVII. fig. 3). 



Station 304 (?). December 31, 1875. Lat. 46° 53' 15" S. Long. 75° 12' W. North- 

 west Patagonia. 45 fathoms. Green sand. 



Shell. — Conical, with a tumid base, a scalar spire, and an impressed suture, uncari- 

 nated, umbilicated, sharply spiralled, thin, brilliantly nacreous, but with a squalid and 

 dirty surface. Sculpture: Longitudinals — there are dense lines of growth and remote 

 puckerings of the surface which might be called bars if they were continuous, but except 

 within the umbilicus they are not uniformly so ; they follow the lines of growth, and are 

 thus very oblique ; they are stronger above than below the periphery. Spirals — Much 

 more marked than the longitudinals are the equal and regularly parted sharp spiral 

 threads which score the whole surface ; of these there are two or three on the earlier 

 whorls, and four on all the later ; where they are crossed by the longitudinal puckerings, 

 they rise into small delicate round white tubercles, which are sparse on the subsutural, 

 and denser on the peripheral threads ; the four spiral threads on the base are feebly 

 dotted, but the two which lie near the umbilicus are somewhat more strongly tubercled 

 than any of the rest ; there are none within the umbilicus. Colour white ; a thin cal- 

 careous layer covers the brilliant nacre of the shell, but is obscured by a dirty deposit 

 which simulates an epidermis. Spire high and scalar. Apex broken. Whorls 6£ remain- 

 ing, of rapid but regular increase, rounded, with a short sloping shoulder above, and 

 constricted below ; very tumid on the base. Suture distinct and impressed by the con- 

 striction of the whorl above it. Mouth very perpendicular, roundly and gibbously oval, 

 bluntly angulated at the insertion of the outer lip, and at the point of the pillar in front, 

 dully nacreous within. Outer lip thin, not descending, well arched. Pillar-Up with a 

 direct edge, concave, bending a good deal over the umbilicus ; it joins the basal lip at an 

 angle just where the spiral thread on the edge of the umbilicus occurs. Umbilicus funnel- 

 shaped and pervious, but a good deal contracted by the convexity of the pdlar ; internally 

 it is scored by longitudinal threadlets, and the strongly impressed suture coils round it 

 within. H. 0-62 in. B. 0"57. Penultimate whorl, height 0'14. Mouth, height 0-31, 

 breadth 0-26. 



I am haunted with the impression of having somewhere seen this species, but can come on no 

 more definite remembrance of it. It is connected with the Trochus ottoi, Phil., group, and is not 

 remote from Trochus (Margarita) infundibulum, W., but is quite certainly distinct. 



1 So called from its squalid appearance. 



