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



Shell. — Small, thin, white, very depressedly conoidal, angulated, tumid on the base, 

 umbilicated ; mouth semioval. Sculpture : It is perfectly smooth but for some curved 

 puckerings which radiate from the umbilicus, but very soon die out ; above the middle the 

 body-whorl is roundly angulated. Colour pure white, with a transparent calcareous layer 

 over brilliant fiery pearly nacre. Spire very depressedly conical. Apex bluntly rounded, 

 with a minute, hyaline, depressed embryonic tip. Wlwrls i\, barely convex. Suture 

 slightly impressed. Mouth semioval. Outer lip thin, barely angulated at the periphery. 

 Pillar-lip straight, patulous, right-angled at its junction with the base. Umbilicus 

 small. H. 0-14 in. B. 0-2, least 0-16. Penultimate whorl, 0-025. Mouth, height 0'09, 

 breadth 0-11. 



The specimen from which I have described this is neither full grown nor perfect, but the species 

 is a very well-marked one. It is much more depressed and has the whorls less rounded than Trochus 

 (Margarita) euspira, Dall. Than Trochus hclicinus, Fabr., it is much more depressed, much more 

 brilliantly nacreous, and the surface is much more polished, and the radiating puckers are much 

 stronger. 



I have put a query to Margarita as the group to which this should be attached, because it has 

 not a rounded mouth ; but there is no other group of Trochus to which it can so well be attached, 

 and none of the characters by which Margarita is defined are very constant. 



57. Trochus (Margarita) cancellatus, Jeffreys. 



Trochus (Margarita) cancellatus, J. Gwyn Jeffreys, "Lightning" and "Porcupine" Moll., Proc. Zool. 



Soc. Lond., 1883, p. 96, No. 4, pi. xx., fig. 4.] 



Station 24. March 25, 1873. Lat. 18° 38' 30" N., long. 65° 5' 30" W. Off Culebra 

 Island, "West Indies. 390 fathoms. Pteropod ooze. 



Habitat. — North Atlantic. Station 16 of "Porcupine" Expedition, 1870. 



This shell can hardly be admitted into the genus Trochus, except, as it were, " under stress of 

 weather." The inner lip is distinctly continuous across the body, and the shell is porcellanous with 

 a lustrous surface within the mouth, but is not, I think, nacreous. The] real difficulty, however, is 

 what else to call it. It recalls Ostoclcs strigatics, Gould. 



58. Trochus (CJirysostoma) px^radoxus (Born). 



Helix paradoxa, Born, Test. Mus. Cass. Vindob., p. 394, pi. xiii. figs. 16, 17. 



Clirysostomus nicobaricus, Chemnitz, Conch. Cab., vol. v. p. 216, pi. 182, figs. 1822-25. 



Turbo nicobaricus, Lamarck, Anim. s. vert., vol. vii. p. 48, and (ed. Desk.) vol. ix. p. 214, sp. 26. 



„ „ Deshayes, Encyclop. method., vol. iii. p. 1098, No. 18 



„ „ Dilhvyn, Cat., vol. ix. p. 816, sp. 3. 



Philippi, Conch. Cab. (ed. Kiister), p. 34, sp. 28, pi. viii. figs. 14-17. 



„ „ Kiener, Iconog. (corrected to Trochus by Fischer, p. 68), No. 45, pi. xxxvi. fig. 5. 



