MARSHALL : ADDITIONS TO " BRITISH CONCHOLOGY." 23! 



approaches O. lukisi, but the suture is not so shelving, and the mouth 

 is larger and grooved. It brings the two species, however, very close 

 together. Although Jeffreys gives this variety as southern and the 

 type as northern, both forms are sometimes found in opposite places. 

 For instance, I have the type from Scilly and the variety from various 

 northern localities. In reality the difference between ordinary 

 northern and southern specimens is hardly sufficient to separate the 

 latter as a distinct variety, for many of those from southern localities 

 will be found to have the same proportions as typical northern speci- 

 mens. But there is a smaller and still more slender form that would 

 have better merited the varietal distinction. It is only a line in length, 

 proportionally narrower than var. australis, and is analogous to O. acuta 

 var. gracilis ; it is rather scarce, but occurs at Jersey, the west of 

 Ireland, the Shetlands, and a few intermediate places. I consider 

 O. tenuis of Jeffreys 1 to be another form of O. cono'idea var. australis. 

 It has no permanent character but that of size to mark it off as a 

 separate species, all those assigned to it by the author being, in my 

 opinion, individual variations only. It is not a thin shell, as its name 

 implies, but is solid for its size, though brittle. Jeffreys' figure of 

 O. tenuis is nearly correct, but the tooth should be stronger and it 

 should have a small umbilical chink. Besides the two stations 

 recorded by Jeffreys, it was dredged at six others by the " Porcupine " 

 Expedition, in some cases in company with O. cono'idea, and the two 

 can be graduated to each other without difficulty. Jeffreys' figure of 

 the type is perfect ; Forbes and Ffanley's answers better for the var. 

 australis ; Sowerby's is good, but is minus the umbilicus. 



O. umbilicaris Malm. — 10 to 60 fathoms, in fine and muddy 

 ground. S.W. Ireland, 37 f. (R.I. A. cruise) ; Tan Spit, Cumbrae 

 (A. Brown) ; Gairloch, 30 f., and Loch Inver 25 f. (Somerville and 

 J. T. M.) ; Liverpool Bay, 12 f. ; Knapdale Lochs, n f. ; Tan Spit, 

 1 of.; Lamlash 17 f. ; Clyde 18 f. ; Skelmorlie 15 f. ; Iona 2of. ; Loch 

 Linnhe 27 f.j Glenelg 60 f. ; Loch Broom 30 f. ; W. Orkneys 45 f. ; 

 E. Shetlands 22 f. 



Var. elongata Jeffr. — Skelmorlie 15 f. j Lamlash 17^3 Gairloch 

 30 f. 



This is a very rare species, and none of the foregoing localities 

 yielded more than two or three specimens. It is most like a stumpy 

 O. acuta, but the latter is more solid and conical, the whorls less tumid, 

 and the last whorl smaller proportionally. It appears to have the 

 same affinity to O. acuta as O. lukisi has to O. cono'idea. There is 

 some variability in the convexity of the whorls and the corresponding 

 depth of the sutural lines, and the apex is not always inverted, but as 



1 Moll. '" Lightning" and " Porcupine," Proc. Zool. Soc, pp. 347-8, pi. 26, fig. 4, 1884. 



