530 The American Naturalist. [July, 
Those with bilateral markings he divided into two subdivisions 
the first comprising those with a central nodule, and the second 
those with none. 
Kuetzing divided the Bacillariacex into three tribes ; I, Stri- 
atx, that is those with transverse striations; II, Vittatz, that is 
those with longitudinal stripes ; and III, Areolatæ, that is those 
whose surfaces are divided into angular areole. The first- 
two tribes, Striate and Vittate he divided into two orders 
each, viz.; I, Astomatice and II, Stomatice. The Astomatice 
included those with no central nodule, or as he understood it, 
with no central opening, while the Stomatice included those 
with a central nodule. If the central nodule were really a 
stoma or aperture as Kuetzing considered it, this grouping 
might have been a natural one; for this difference in structure 
might have connoted important physiological differences, but 
it is generally conceded that the nodules are merely markings 
on the valves, and it is likely that they indicate nothing as to 
the physiology of the plant. Sono higher groups than genera, 
or possibly species, can be based on this character. His third 
tribe, Areolatx, he also divided into two orders; I, Disciformex 
that is, those of a circular or angular form, and, II, Appendi- 
culate, or forms with appendages, as Biddulphia. 
The classification of Prof. H. L. Smith‘ is one that has had 
considerable following. Bessey’s Botany® was the first American 
textbook to adopt and give an outline of the system. It was 
adopted by Van Heurck®, Wolle and De Toni®. To say the 
least, it is a good practical system of classification, and prob- 
ably this is the most that can be said for it, though in some 
points it seems to approach a natural system. Smith divides 
the Diatoms into three tribes, the Raphidex, Pseudoraphidee, 
and Cryptoraphidex. The Raphidex are all supposed to possess 
a raphe. The Pseudoraphidex are usually elongated, have no 
raphe, but in its place there is a blank space resembling a 
t Conspectus of the Families and Genera of the Diatomacee in The Lens, I: 1 
1872 and II: 65, 1873. 
5 Botany for High Schools and Colleges, pi Holt and Co., New York, 1880, 
ê Synopsis des Diatomées de Belgique, 188 
1 Diatomaceæ of North America, 1890. 
8 Sylloge Algarum, 1891. 
