476 Mr. C. Mereschkowsky on Californian Diatoms. 
119. Nitzschiella longissima (Bréb.), Ralfs. San Pedro, not 
very common. [M.] 
120. Nitzschiella biplacata, var. pacifica, nov. var. (Pl. IV. 
figs. 15-17.) San Pedro, very common. [M.] 
In the Black Sea I have repeatedly observed a form greatly 
resembling N. /ongissima, but much smaller and more delicate, 
varying in length from 0-060 mm. to 0°175 mm., while 
N, longissima varies from 0°162 to 0-483 mm. The main 
difference between these two forms consists, however, in the 
endochrome, which in JV. longiss¢ma is composed of numerous 
elongated bacilliform granules, while in the small form there 
are two plates, a difference which shows that they are speci- 
fically different. This smaller species, which I have named 
N. biplacata*, is the same which Van Heurck, not knowing 
of the difference existing in the endochrome, has mentioned 
in his treatise on the Diatomacee (p. 404) simply as a form 
(forma parva) of N. longissima. 
In the Pacific I have found a variety of N. biplacata which 
is smaller and has a much broader girdle-face (fig. 16); the 
latter has a very different appearance from the vale: face 
(figs. 15,17). ‘he rostra are usually quite straight, their 
apices sometimes inflated, sometimes not. Endochrome com- 
posed of two plates. While moving the frustule does not 
turn around its longitudinal axis. Length 0°056-0:098 mm., 
breadth of the valve 0:006-0:0065 mm., of the girdle-face in 
the middle 0-0U58-0'0L mm. (usually 0-01), at the apices 
0:003-0°0055 mm. 
121. Nitzschiella tenuirostris, Mer. (PI. IV. figs. 1-3.) San 
Pedro, common. [M.] 
Under the name of JV. clostertum there have been con- 
founded a number of forms belonging partly to 1. tenud- 
rostris, partly to another species (N. gracilis, Mer.) ; and as 
it is impossible to know what the different authors meant by 
this name, I proposed in my paper on the Diatoms of the 
Black Sea a new arrangement of the various forms belonging 
to this group, in which, i in order to avoid confusion, [I aban- 
doned the old name closter’um. Under the name N. tenut- 
rostris 1 understand the following form :— 
Valve fusiform, abruptly terminating in long very fine 
rostra, slightly curved on the same side, the whole frustule 
being arcuate. Stria and carinal dots invisible. Girdle-face 
not differing from the valve-face. Endochrome composed of 
two plates. General length 0082-0180 mm. (usually 
* See my paper on the Diatoms of the Black Sea. 
