MARSHALL: ADDITIONS TO "BRITISH CONCHOLOGY." 169 



more specimens of this rare mollusc that are brought to light by deep 

 dredging, the greater appears its range of variability. My Dornoch 

 specimen is slender, like Jeffreys' and Sowerby's figures ; but in the 

 Shetland specimens, which I consider the type, the lower whorls are 

 broader and more convex, and the upper ones proportionally more 

 slender. Sars gives a figure double the length of our shell, showing a 

 lengthened cone regularly proportioned, without the pinched-up apex 

 or the peculiar aperture ; similar specimens to this were dredged by 

 the 'Porcupine' off the coast of Portugal in 1,095 fathoms. Other 

 specimens procured by the 'Porcupine' Expedition show a great varia- 

 tion in size, as in the last species, some being three times the size of 

 British examples, with others dwindling down to the var. minor of 

 Jeffreys (A. exigua G. O. Sars); while other forms from very deep 

 water in the Atlantic are sculptured, some with spiral and others with 

 longitudinal striae. An analogous case to the latter occurs in Cithna 

 tenella, which was described and is usually found to be a smooth shell, 

 but specimens of which dredged by the 'Challenger' and 'Porcupine' 

 were found to be more or less striated, longitudinally or spirally. I 

 have also two specimens of another smooth species, Pherusa gulsonce, 

 from deep water in the Mediterranean, that are sculptured with two 

 spiral stria; round the periphery and one at the base of the upper 

 whorls. 



Pherusa gulsonae Ok. — 12 to 90 f. in fine sand. Isle of Man 

 (L.M.B.C.)! Arran Isles (Barlee); Loch Boisdale, 15 f., and Sound 

 ofSleat, 80 — 90 f. (Somerville and J.T.M.) ; Jersey; Scilly ; Land's 

 End ; Eddystone ; Borough Island ; Torbay ; off Dawlish ; Bere- 

 haven ; Connemara ; Iona; N. Sutherlandshire ; W. Orkneys, 45 f.; 

 Pentland Frith, 35 f. Also Vigo Bay, 20 f. ; off Tangiers, 335 f. ; 

 and Pantellaria, 390 f. ('Porcupine') ! 



Var. tenuicula Jeffr. — Guernsey ; Scilly Isles ; St. Ives ; Fal- 

 mouth ; Berehaven ; N. Sutherlandshire ; W. Orkneys; E. Shetlands. 



There are three sizes of this shell — one is 0*125 ^ ncn m length, 

 which I have from Guernsey only ; the second is of the dimensions 

 given by Jeffreys, and the third is the dwarf form tenuicula. Mr. 

 Clark in his description ascribes to this species a rudimentary tooth, 

 but I have found no sign of it in at least a hundred specimens. 

 There is no difficulty in identifying the species so long as the aperture 

 is perfect ; it is remarkably expanded outwards, and like no other 

 except A. walleri; but when broken off, to which accident it is very 

 liable, its aspect is entirely altered, and it looks more like Odostomia 

 nivosa. Immature specimens of course have not the expanded outer 

 lip, and in this stage they very closely resemble O. minima, the only 

 differences being that the latter has a more pointed apex and a more 

 slender spire. 



