80 THE VOYAGE OF H.M.S. CHALLENGER 



becomes feebler, these threads become extremely numerous and crowded. Colour yellowish 

 chalky white over brilliant nacre. Spire not much elevated, but a little scalar. Apex 

 eroded. Whorls 5, rounded, of rapid increase, inflated on the base. Suture impressed 

 near the apex, while towards the mouth it becomes filled up, and is finally marginated, by 

 the last whorl lapping up rather coarsely on the previous one. Mouth rather oblique, a 

 little higher than it is broad, slightly flattened above, and a very little angulated at the 

 insertion of the outer lip. Lip thin, a very little reflected on the umbilicus, porcellanous 

 on the edge, with a very slight pearly marginal callus, which is continuous across the 

 body, and nacreous within. Umbilicus large, funnel-shaped, quickly contracting, but 

 leaving the whole inner spire visible. H. 0*38 in. B. 0*4, least "33. Penultimate whorl. 

 0-1. Mouth, height 0-23, breadth 0'2. 



Both in form and texture this species is extraordinarily like a depressed Cyclostoma. I have 

 given it its name, in the absence of marked features, from its slight resemblance to a bubble. It 

 has some resemblance to Trochus rhina, Wats., when, as sometimes in that species, the sculpture is 

 exceptionally obsolete ; but the sculpture is still very obviously different, and the form is globose, not, 

 as in that species, high and conical. 



46. Trochus {Margarita) rhina, 1 Watson (PI. V. fig. 1). 



Trochus (Margarita) lima, Watson, Prelim. Eeport, pt. 4, Journ. Linn. Soc. Lond., vol. xiv. p. 703 



(nee Phil.) 



Station 73. June 30, 1873. Lat, 38° 30' N., long. 31° 14' W. W. of Azores. 

 1000 fathoms. Pteropod ooze. 



Station 75. July 2, 1873. Lat. 38° 38' N., long. 28° 28' 30" W. Fayal, Azores. 

 450 fathoms. Volcanic mud. 



Station 78. July 10, 1873. Lat. 37° 26' N., long. 25° 13' W. San Miguel, Azores. 

 1000 fathoms. Volcanic mud. 



Shell. — Conical, with a broad and tumid base and a wide narrowed umbilicus ; sur- 

 face cross-hatched like a file; when fresh, translucent with a pearly sheen. Sculpture: 

 Spirals — there are three to five slightly raised remotely beaded threads, of which one lies 

 a little below the suture, one at the periphery forming a carina, of which the beads are 

 much smaller and closer set, sometimes evanescent ; one, with beads like the first, defines 

 the umbilicus, within which there is a strong spiral ridge ; and the whole surface is covered 

 with fine rather sharp threads, whose partings are twice as broad as themselves. Of these 

 finer spirals, the one which meets the outer lip often rises into prominence and defines the 

 base, while another above the carina sometimes stands out more strongly and more beaded 



1 g/nj, a file. The preoccupation by Philippi of the name I bad chosen necessitates this change from lima 

 to its Greek equivalent. 



