90 THE VOYAGE OF H.M.S. CHALLENGER. 



54. Trochus (Margarita) dnopherus, 1 Watson (PI. V. fig. 3). 



Trochus {Margarita) dnoplierus, Watson, Prelim. Report, pt. 4, Journ. Linn. Soc. Lond., voL xiv. 



p. 711. 



Station 122. September 10, 1873. Lat. 9° 5' S., long. 34° 49' W. Off Pernambuco. 

 350 fathoms. Red mud. 



Shell. — Depressedly conical, rather strong, semi-transparent, of a dark pearly iridescence. 

 Sculpture: There are spiral ridges, strong, five above the base ; the first is close to the 

 suture, and is exquisitely beaded from the middle of the second whorl ; the beads are 

 about thirty-five on the last, twenty-two on the penultimate whorl. The second ridge is 

 remote from the first, and forms a shoulder to the whorls. The third, fourth, and fifth 

 occupy the periphery, which is carinated by the fourth till close up to the mouth, when 

 the fifth forms the carina. Four fine threads, of which the first is partially beaded, lie in 

 the flat between the first and second ridges ; two between the second and third ; one 

 between the third and fourth. Below the fifth rido-e is a flat furrow narrower than the 

 rest : below the furrow is a sixth ridsre. slip-liter than the others ; and then the base is 

 closely covered with eleven spiral threads, which tend to become stronger and wider apart 

 near the umbilicus. The first three ridges alone appear on the upper whorls. Longitu- 

 dinally the whole surface is sharply scored by the lines of growth. Colour a ruddy 

 brownish white, shot with a purple and green iridescence. Spire depressedly scalar. 

 Apex bluntly mammillated by the somewhat shapeless, round, largish, glassy, ruddy, 

 embryonic whorl. Whorls A\, of rather rapid increase. Suture somewhat faiut. Mouth 

 oblique, roundish, being slightly peaked above and a little angulated on the pillar. 

 Outer lip sharp but not thin, brilliantly iridescent within. Inner lip very much thickened 

 by a pearly pad, which is very thick below where it envelops what might otherwise have 

 been a tooth on the point of the pillar. The pad is thinner in the middle of the pillar, 

 and thickens again at the junction with the body-whorl, on which it thins out quickly. 

 The lip here is very slightly reflected on the umbilicus. Umbilicus very small and con- 

 tracted, not so much by the reflection of the inner lip as by the pillar being bent round 

 across it. Operculum very thin, yellow, horny, with about eleven very faintly defined 

 turns. H. 0"28 in. B. 0-37, least 0*26. Penultimate whorl, 0-08. Mouth, height 0*2, 

 breadth 0*2. 



This species has a close general resemblance to Margarita dbscura, Couth., but that is smaller, of 

 slower increase, has an open umbilicus, is very dull in colour, and has much fewer spirals, besides 

 which the whole minute system of spirals is different ; the tubercled spiral, in particular, is the second, 

 not the first, as here, and is not close to the suture. Than Margarita poculosa, Gould, which it 

 resembles in its style of spirals, this is more discoidal, and is especially more tabulated below the 

 suture ; the angulation here is on the upper, not on the lower part of the whorls, and in that the 

 infra-sutural thread is not beaded. 



btocfiigo;, dusky. 



