28 
In a paper of this character, intended to guide observers in ther : 
determination of genera, it is sincerely to be regretted that the 
author did not follow the classification of Prof. H. L. Smith, now 
so generally accepted. A number of the generic names men- | 
tioned are so ancient that their use is likely to create confusion, 
The division into fresh water and marine genera is not at all | 
a happy one. Of the thirty-four genera enumerated on page 98 
as fresh water, eleven are also marine, while two others,— Zé erp. 
sinoé and Schizonema—are exclusively marine. Nearly all the! 
species of Pleurosigma, also, are either marine or brackish. As: 
Navicula, Surirella, Campylodiscus, Synedra, Melosira, Niteschia, 
Cocconeis and Achnanthes are given among the fresh water and_ 
omitted from the marine genera, it is evident that the author | 
ranks these as exclusively fresh-water forms. This is quite in- 
correct, as the number of marine species belonging to the genera 
named is, in most of them, even more numerous than the fresh- 
water species. Some of the most interesting forms commonly 
found in marine collections, are conspicuously absent from the list 
of marine genera, as, for instance, Coscinodiscus, Amphiprora, 
Actinoptychus and Actinocyclus. It is true that three of these 
are mentioned in the list of fossil forms, but then it is not made 
clear that the list of fossil forms given represents a marine depos- 
it. Surely the writer must be aware of the fact that there are. 
fresh water as well as marine deposits. 
While the descriptions of genera were not intended to be m 
nutely accurate, yet some of them are so loose as to be mislead: | 
ing’ For instance, in telling how to distinguish Campylodiscus 
Surirella and Cymatopleura, the statement is made that if the 
frustule is twisted the specimen is a Campylodiscus. This would 
sadly puzzle a beginner, for Surirella and Cymatopleura are also 
frequently twisted. The word “ twisted” has been used tod 
scribe the shape of a Campylodiscus, but, to most minds, the old 
term “saddle-shaped ” would be more expressive. | 
Perhaps it may not be amiss to add in conclusion that there 
is certainly no better guide to the determination of genera than 
is given in the “ Conspectus of the Diatomacez,” by Prof. H 
L. Sniith, first published in “The Lens,” in 1872, but lately te 
printed by Dr, Wolle in his work on The Diatomacee of North 
America. C.H. Ke - 
