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II. — An Essay on the Classification of the Diatomacete. 
By M. Paul Petit. Translated by F. Kitton, Hon. F.K.M.S. 
{Taken as read before the Royal Microscopical Society, June 6, 1877.) 
( Continued from page 14.) 
Plates CLXXXVII. and CLXXXVIII. 
Part II. 
In the preceding part the author gave an explanation of his method 
of classification ; he then proceeds to describe the typical forms of 
the sixteen tribes into which the two sub-families are divided. — F. K. 
1st Sub-family, Placochromatice.e. Frustules furnished 
with a lamellate endochrome. 
1st Tribe, Achnanthe.e. 
This tribe is the same as Herr Grunow’s (minus the genus 
Bhoicosphenia, which I again place with the Gomphonemeae), and 
comprehends the genera Cocconeis and Achnanthes of Dr. Pfitzer. 
It contains the diatoms that have their frustules arched or geni- 
culate and the two valves unsymmetrical, one of which is convex 
and the other concave, the latter only having a central nodule. 
The endochrome consists of a very thick single layer placed on the 
internal surface of one of the two valves, the other remaining 
independent. 
I have been able to verify this disposition of the endochrome in 
Achnanthes longipes Ag. This species conforms to the common 
law, although Dr. Pfitzer * says that the endochrome is broken up 
into a great quantity of small fragments. This condition may be 
observed, but only when the Achnanthes have been some time out 
of the sea, the plasma altering very rapidly. [Dr. Pfitzer is not 
positive of this ; he says, “ Bei den wenigen Exemplaren von 
A. longipes Ag. welche mir vorkamen, waren die Endochromplatten 
in viele kleinere Theile zerschnitten ich muss dahin gestellt sein 
lassen, ob dies ein normaler Zustand war.” — F. K.] 
Genera, Cocconeis, Achnanthidium, Achnanthes. 
2nd Tribe, Gojiphonehe.e, 
contains two genera only. This tribe is connected with the pre- 
ceding by the genus Bhoicosphenia Grun. 
This genus, like Achnanthes, has the valves non-symmetrical, 
bent or geniculate, and only one of them has a central nodule ; but 
the frustule is cuneiform, like the other Gomphonemas, and the 
endochrome consists of a single layer resting on one of the scales 
* Loc. cit., p. 85. 
