MARSHALL: ADDITIONS TO "BRITISH CONCHOLOGY." 337 



O. ventricosa Forb. {J. Conch., vol. 7, p. 255-6, 1893). — Fine 

 sandy mud, 15-80 f., from Jersey to Shetland. 



This is not a satisfactory species, some forms being difficult to 

 separate from the last, but usually this is thinner, more conical, and 

 the whorls more convex, while in O. acicula the upper whorls are 

 more rapidly formed and the lower ones are uniform in width, 

 imparting a cylindrical outline; but it must be noted that these 

 characters are occasionally reversed, some specimens of O. acicula 

 having also convex whorls, especially on the lower halt, while others of 

 O. ventricosa have a cylindrical outline, with the whorls more or less 

 compressed, either in the middle or on the upper part only of each 

 whorl, or they are compressed throughout. Sowerby's figure of O. 

 acicula represents one of these compressed 0. ventricosa. The best 

 typical specimens are dredged in the sheltered lochs of the Hebrides; 

 these are very thin and polished, nearly transparent, regularly conical, 

 and easily separable from O. acicula ; but some difficulty will be 

 experienced especially with those from the Channel and Scilly Islands, 

 which are more solid, cylindrical, and compressed, these characters 

 interchanging in a most perplexing manner with O. acicula. It is 

 more local than that species, but comparatively plentiful in some parts 

 of the Hebrides. Both Jeffreys' and Sowerby's figures are very good, 

 though the latter has too many whorls. 



O. nitidissima Mont. — Fine sand, 5-45 f. Scilly Islands (Bur- 

 kill and J.T.M.); off Millport, Cumbrae (Knight)! Dornoch Frith 

 (Baillie and J.T.M.); Jersey and Sark ; the Minch 40 f. ; Orkneys, 

 45 f. Fossil in the Belfast deposit (Praeger) ! 



It is remarkable that this species, whose extreme slenderness is its 

 most striking feature, should also possess a broader as well as a more 

 slender relative ; the latter, which is hardly more than half the width 

 of the type, sparingly occurs almost everywhere with it, but those from 

 the west of Ireland coasts all belong to the slender form. A rare 

 form has compressed whorls and a shallower suture, and a monstrosity 

 has the whorls carinated. Living specimens are yellowish-brown. 

 Sowerby's good figure is the type form ; Jeffreys', equally good, is the 

 Irish or slender one. Specimens without the microscopical spiral 

 striae occasionally occur on the British coasts ; this is 0. pointeli De 

 Fo\in=0. nitidissima var. pura Monts. 



A specimen of O. nitens Jeffr. was dredged by the " Triton " in the 

 Shetland-Fserce Channel, 570 f. ! 



O. fallax Monter. {Bull Mall. Ital., p. 70, i88o)=0. suboblonga 

 Jeffr. (Proc. Zool. Soc, p. 345, pi. xxvi.,f. 3, 1884). — I detected a speci- 

 men of this shell among some of the dredgings of the Royal Irish 

 Academy cruise of 1886 off S.W. Ireland, from 48 f. It was also 



