284 



ADDITIONS TO "BRITISH CONCHOLOGY." 



(Continued trom page 232). 



By J. T. MARSHALL. 



Odostomia (continued). 



O. conspicua Aid. — 9 to 50 fathoms, in shelly and gravelly sand. 

 Scilly Islands 40 f. (Smart and others) ; S.W. Ireland 54 f. (R.I.A. 

 cruise) ; Loch Craignish 9 f . (Somerville) ! Oban 18 — 25 f., and Loch 

 Inver 25 f. (Somerville and J.T. M.); Falmouth 19 f. ; Lamlash Bay 

 17 f. ; Loch Fyne 20 f. ; Glenelg 50 f. ; the Minch 45 f. ; Pentland 

 Frith 35 f. 



This is an exceedingly solid shell, and not variable. It can only be 

 confused, and then in the immature stage, with O. unidentata, when 

 it will cause some trouble ; but a specimen the size of the latter has 

 the spire more tapering, the whorls not so compact, the apex or 

 embryonic whorls larger and blunter, and the base of the mouth pro- 

 duced. The tooth appears small for the size of the shell viewed 

 externally, but when the outer lip is broken away it is seen to be 

 unusually large and strong. The mouth in the young is not grooved ; 

 and in the adult the grooves are fewer and fainter than in O. condidea. 

 Although widely diffused in Great Britian, it is rare and scarcely ever 

 dredged alive. I have found it less rare in the Scilly Islands than 

 elsewhere, but they are a smaller form, and white. A fine specimen 

 from Guernsey has compressed whorls and a shallow suture ; this 

 peculiar variation seems to run more or less through many of the 

 members of this section. Mr. Somerville's Craignish specimen was 

 living, a third of an inch in length, and still immature. The following 

 description of the operculum was taken from it — Having four whorls, 

 with the usual slit for the reception of the tooth (which is large and 

 projecting), the last whorl coarsely wrinkled; length r-2oth of an inch, 

 and small for the size of the aperture. It is very like that of 

 O. condidea, but the striation and the groove for the tooth are unusually 

 conspicuous. 



All the published figures agree in being very good ones. Jeffreys 

 has no dimensions attached to his, but it should be one-third of an 

 inch in length. 



O. unidentata Mont. — This may always be known from O. acuta, 

 its nearest congener, by the absence of an umbilicus and a squarish 

 mouth. It is not at all variable, and its characters are pretty constant, 

 what variability it has being in the contour of the whorls, prominence 

 of the tooth, and angularity of the base. The apical whorls are not 

 exposed horizontally as in the last species, but only partly so, . and 

 partly intorted, as in the next. A single specimen has been found in 

 the Belfast clays (Praeger) ! 



