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of the zone, and covering the two valves and the other side of the 
zone, in the middle of which is found the line of separation. This 
disposition of the endochrome characterizes the Gomphonemese. 
Genera, Rhoicosphenia, Gomphonema. 
3rd Tribe, Cymbelleae. 
The Cymbelleae comprises all the genera having the valves 
cymbiform or arched, and the endochrome disposed exactly the 
same as found in Gomphonemeae. The layer sometimes rests on 
the convex and sometimes on the concave zone ; this particularly 
serves to distinguish the difference between the genera. I follow 
the example of Dr. Pfitzer in connecting Epithemia with Amphora ; 
but all of them require further study. 
Genera, Cocconema, Cymbella, Encyonema, Amphora, Epi- 
themia, Brehissonia Grun. 
4th Tribe, Naviculeae. 
This tribe includes the genera having generally symmetrical 
valves and without keels, the endochrome of which is divided into 
two layers resting on each side of the zone with two lines of sepa- 
ration. The genera differ only by the slightest modifications which 
the endochrome undergoes. 
The Cymbelleae approach the Naviculeae through the genus 
Brehissonia Grun. [This genus was constituted to receive the 
form named by Ehrenberg * Gymbella Boeckii = Gomphonema 
lanceolatum Ag. f = Dorypliora Boeckii Smith. | Professor H. L. 
Smith § refers it to Navicula. — F. K.] It has the symmetrical valves 
of the latter and the endochrome of the Cymbelleae. 
Navicula sphserophora (Kutz.) = Anomoeoneis spheerophora 
Pfitzer, is the link on the side of the Naviculeae. Dr. Pfitzer has 
created a new genus for the reception of this species, having 
remarked a blank space in the striation on one side of the central 
nodule, this want of symmetry establishing the relationship of 
this species with the Cymbelleae. The characters furnished by the 
endochrome, according to Dr. Pfitzer, differ completely from those of 
N. ambigua Ehr., a species some authors are disposed to unite to 
N. spheerophora Ktz.|| [ N . ambigua, if the character of the 
striation is of any specific value, should be placed near to N. cus- 
pidata, as its longitudinal strife closely resemble those on that 
form. — F. K.] But Dr. Pfitzer does not say if the disposition of the 
endochrome is constant, but that the fault in the striation is found 
on individuals from various localities. For myself, I have not been 
able to verify the fact, neither on the specimens I have collected at 
* ‘ Infusionsthierchen,’ tafel 19, fig. 5. f Agardh’s ‘ Conspectus,’ p. 34. 
t ‘ Synopsis British Diatomaceae,’ i. p. 77. § ‘ Lens,’ vol. i. pp. 77, 78. 
|| Rabenhorst, ‘ FI. Europ. Algarum,’ p. 192. 
