I70 JOURNAL OF CONCHOLOGY, VOL. 9, NO. 6, APRIL, 1899. 



I do not know of any good figure of this species. Jeffreys' is bad, 

 and badly executed, and only likely to mislead the student. Sowerby's 

 is nothing like. Forbes and Hanley's has some resemblance to it, but 

 it is not slender enough, and the aperture is incorrect. 



Odostomia Flem. — An accurate knowledge of this difficult and 

 prolific genus is not to be learnt or taught by the most concise de- 

 scriptions or from the most accurate of plates, but by an extended 

 experience in the examination of large numbers of specimens from 

 various localities, and by an intimate acquaintance with them both in 

 the field and in the study. There is no short cut to it. The difficul- 

 ties of identification are caused principally by the smooth members 

 of the genus possessing such few points of distinction, and these diffi- 

 culties are enhanced not only by the presence of varieties and of 

 intermediate and immature forms, but by those individual and sexual 

 variations which exist in all univalve species, of having a shorter and 

 also a more slender form than the type, as well as a longer and a 

 shorter one, even the varieties presenting the same mutations. It is 

 these latter, more emphasized in some species than in others, which 

 form the groundwork of many of our named varieties, especially in the 

 Odostomitz. In some species, where the sexes are separate, this varia- 

 tion only indicates the male and female ; but the rule will be found 

 to obtain in all species, univalve and bivalve. (Among bivalves, this 

 rule of variation exhibits not only a more globular and also a more 

 depressed form than the type, but likewise a longer and a broader form). 

 It is becoming more and more realised that to obtain a practical know- 

 ledge of any given group or species, a large number of specimens 

 from different localities must be examined, so as to obtain the range 

 of individual variation before generalising. No one, for example, 

 could write with any authority on the genus Homo by merely examin- 

 ing a couple, a dozen, or a hundred examples ; but the more there 

 are examined, the more expansive becomes one's ideas of their capaci- 

 ties for variation up to certain definable limits. 



Jeffreys' descriptions of the Odostomia are excellent, and leave 

 nothing to be desired so far as conciseness and fulness go ; but in 

 many critical species such a close comparison of the details is neces- 

 sary that they should be read side by side, which is of course impos- 

 sible in a bound volume ; and although in many instances the author 

 mentions in the text the main points in which they differ, these are 

 sometimes too short to be serviceable. The figures of the Odostomice 

 in " British Conchology," though not badly drawn, are very badly 

 printed, while those in "British Mollusca" are admirably drawn and 

 printed, but do not always correctly represent the type forms — in 

 some cases they even misrepresent them ; and the same must be said 



