On the Classification of the Diatomacese. By M. Paul Petit. 71 
of the zone, and are divided towards the centre by a deep furrow 
spread out perpendicularly towards the valve. This character and 
the form of the valves are sufficient to distinguish the Synedras from 
the Eunotias. 
Genera, Eunotia, Himantidium. 
2nd Sub -family, Coccochromatice^e. Frustules containing a 
granular endochrome. 
10th Tribe, Fragilarie® (Fig. 21). 
This tribe contains the species very closely related to the 
Eunotieae and Synedreae through the form of the frustules. On 
the other hand, in the two last tribes (which strictly should form 
but one) we see that the endochrome shows a tendency to divide. 
In the Fragilariese we now meet with the endochrome divided into 
a great number of small layers, and we find it distinctly granular 
(Fig. 21). 
The genera Fragilaria and Odontidium, through the study 
of their endochrome, must be again revised, as a great number of 
their species ought to be placed among the Placochromaticees. 
Ex. : F. capucina Desm., 0. mutabile W. Sm., and 0. tabellaria 
W. Sm. 
As to the genus Diatoma, of which Dr. Pfitzer would even 
abolish the name, I believe it must be preserved, because it has 
given the name to the family, and, moreover, it offers some very 
decided characters. In spite of the very good reasons that he is 
able to give, it would be impossible to change the generally ad- 
mitted name of Diatomacese to that of Bacillaria, which is only 
employed by a small number of German authors. 
Genera, Fragilaria, Diatoma, and a number of marine genera. 
11th Tribe, Meridiem (Fig. 22). 
The disposition of the granular endochrome on the internal 
surface of the valves is the same as that found in the preceding 
tribe, but in the Meridieae the frustules are cuneiform — a parti- 
cularity which is sensibly apparent in many varieties of the genus 
Diatoma. It is therefore through this genus that the passage of 
one tribe into the other takes place. 
Genera, Meridion, Eucampia. 
[Meridion is placed in the genus Diatoma by Professor H. L. 
Smith* The cuneate form of the frustules is not constant. Pro- 
fessor Smith has sent me specimens in which the frustules form 
straight filaments like a Fragilaria. The species of this genus 
bear a strong resemblance to Odontidium anomalum, as noticed 
* 1 Lens,’ vol. i. p. 83. 
