CHASTER AND HEATHCOTE : MOLLUSCA OF OBAN. 299 



O. unidentata, Mont. [A,M.N. j. Occurred sparingly live 



and dead in the dredged material. 

 ** O. turrita, Hanley. Dredged dead. 

 ** O. nivosa, Mont. Two dead specimens dredged. 

 ** O. pallida, Mont. A few examples were taken alive from 

 the ears of Pecten opercularis dredged near Fraoich Island. 

 The reason of this commensalism may be as Jeffreys 

 suggests, that the Odostoiuia subsists on the fcecal matter 

 of the scallop, or, as seems quite as likely, that the active 

 movements of the latter constantly carry the little gastropod 

 to ' fresh woods and pastures new,' where provision may 

 be brought within reach of its toothless mouth. It is 

 ensconced on the only part of the Pecten from which it is not 

 liable to be ousted during the erratic flights of the latter. 



We cannot refrain from here quoting Clark's remarks 

 on this species and the so called species rissoides and 

 albella. ' We have not the slightest doubt that the Che/n- 

 nitzia rissoides__\s a dwarf littoral variety of the pallida. 

 A comparison of our notes on these two animals bear us out 

 in this view ; these two alone agree, whilst every other 

 exhibits some difference. . . . This rissoideaft variety 

 of Chem. pallida is the parent of the C. albella and C. 

 dubia of authors.' Our own observations of these forms 

 bring us into complete accordance with the views of our 

 most competent marine malacologist. 

 * O. umbilicaris, Malm. [Jeffreys; A.M.N.]. Very rare in 



Clyde district (Brown). 

 O. lukisi, Jeff, [dredged in 20—25 f, Jeffreys; A. M.N.J. 

 One live and two dead specimens in the dredged material. 

 lu addition to the general shape and other characters given 

 in ' British Conchology,' a careful examination of the apex 

 of the shell gives a ready means of recognition. The first 

 whorl visible in side view is keeled above, this keel sur- 

 rounding a small concavity in which, when looked at from 



