96 DR. GWYN JEFFREYS ON THE MOLLUSCA OF THE [Mar. 6, 



there are about 40 on the last whorl, some of them double ; the in- 

 terstices are quite smooth : colour light yellowish-brown : spire 

 raised : whorls 6, convex and rounded ; the last is equal to about 

 two fifths of the spire ; apex twisted : suture distinct : mouthn&&r\y 

 circular; outer lip tliin, but thicker and expanded at the base and 

 partly folded over the umbilical perforation : umbilicus somewhat 

 concave, with a small perforation. L. 0"15, B. O'l. 



'Porcupine' Exp. 1870: Atl. St. 16, !/«. Two specimens, one 

 imperfect and the other not full-grown. 



4. Trochus cancellatus^ Jeffreys. (Plate XX. fig. 4.) 



Shell, forming a depressed cone, rather thin, opaque, and 

 lustreless : sculpture, oblique laminar ribs in the line of growth, 

 which are crossed by as many but shghter spiral striae ; there are 

 about 20 ribs and strise on the last whorl ; this sculpture covers 

 the base, but the striae are wanting on the apex : colour pale 

 yellowish-brown : spire rather depressed : whorls 5-6, convex ; the 

 last occupies three fifths of the shell ; apex regular and compressed : 

 mouth more round than oval, angulated above and below on the inner 

 side : outer lip somewhat expanded and thickened : inner lip nearly 

 straight, attached to the pillar below the periphery : umbilicus 

 rather narrow, with a deep perforation which exposes the inner 

 whorls. L. 0-1, B. 015. 



'Porcupine' Exp. 18/0 : Atl. St. 16. A single specimen. 



Distribution. Josephine Bank ('Josephine' Exp.) ; 340-430 fms. 



This and the following five species, or some of them, belong to 

 the genus 3Iach(eroplax of Friele, which chiefly depends on the form 

 of the radula or odontophore. 



[^ 5. Trochus cinereus, Couthouy. 



Turbo cinereus. Couth, in Boston Journ. Nat. Hist. vol. ii. 

 p. 99, pi. 3. f. 9 (1839). 



Trochus cinereus, B. C. iii. p. 304 ; v. p. 202. 



'Porcupine' Exp. 1869: St. 14. A young and dead specimen, 

 but apparently recent. 



Distribution. Arctic seas in both hemispheres, from Spitzbergen 

 and Iceland to Floroe near Bergen and the Siberian coast, and from 

 W. and E. Greenland to C. Cod, and Behring Str. to Sitka; 5-150 

 fms. 



Fossil. Post-tertiary : Scandinavia, Shetland, E. and W. Scotland, 

 Ireland, N. America, and Sicily?; 0-460 ft. 



Margarita striata of Broderip and Sowerby (1828-29), but not 

 Trochus striatus of Linn6, possibly M. arctica of Leach (1819) and 

 T. leachii of Philippi, and il/. sordida of Hancock. As fossil, per- 

 haps T. granatelli of Calcara. Leach's description is indeterminable, 

 viz. : — "M. purpurascente carnea tenuiter striolata, operculotestaceo." 



The animal has been described by me (in the 'Annals and Magazine 

 of Nat. Hist.' for March 1877), and the odontophore by Friele. 



' Cross-barred. 



