24 W. M. BALE ON SOME OF THE DISCOID DIATOMS. 



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The structure of the valve-border is a feature which has not 

 always received sufficient attention from observers, who have 

 overlooked peculiarities which might be of service in classification. 

 This refers to the general character of the border, and more 

 particularly to the minute appendages which it frequently bears. 

 The apiculi which form a circlet at the margin of many species 

 are familiar to all observers, more especially those which in some 

 of the Fasciculati and Cestodiscoidales attain a prominence which 

 could not fail to attract attention. But those which are 

 asymmetrical, and of which only one or two appear on each valve, 

 have hitherto singularly escaped notice, except in a very few 

 instances, where they are more conspicuous than usual. For 

 example, in the robust form of C. lineatus, described as C. leptopus, 

 a single larger apiculus, farther in than the rest, is quoted by 

 Rattray as distinguishing C. leptopus from its allies. Y~et in 

 fact it is not peculiar to this form, a similar apiculus, but more 

 delicate, being easily discoverable in other and more nearly 

 typical forms of C. lineatus. Further, it is equally a feature of 

 C. excentricus, and I find it commonly present, though apparently 

 hitherto unnoticed, in forms of that species from such different 

 localities as Port Phillip, Cuxhaven, Santa Monica, and Peru and 

 Bolivia guanos. (There is, of course, no justification for the line 

 of demarcation drawn by Battray between the respective groups 

 of the Lineati and the Excentrici. The two type species are con- 

 nected by intermediate forms, and the same remark applies to 

 C. excentricus and C. subtilis.) 



Among the Badiati the tendency is towards the production of 

 two apiculi, which occupy positions about one-third or one-fourth 

 of the circumference apart. They are found in many species,, 

 though strangely enough I can find no mention of them by any 

 observer except in the cases of G. concinnus and C. centralis, in 

 both of which forms they are very conspicuous. Battray says 

 that C. centralis is distinguished from C. asteromphalus by these 

 apiculi, and cannot be united with it in the same species, as pro- 

 posed by Grunow. An unfortunate dictum, since all, or nearly 

 all, of the numerous varieties of C. asteromphalus agree precisely 

 with C. centralis in this respect, while such apiculi, but more 

 rudimentary and indefinite, are found in a wide range of forms 

 comprised under C. marginatus, C. perforates, C. apiculatus r 

 C. borealis and others. Their minute size and indefinite form 



