•476 ]\Ir. C. Mereschkowsky on Califomian Diatoms. 



119. Nitzschiella longissima (Breb.), Ralfs. San Pedro, not 



very ciMiinioii. [M.] 



120. Nitzschiella biplacata, var. pacifica, nov. var. (PI. IV. 

 figs. 15-17.) San Pedro, very common. [M.] 



In tlie Black Sea I have repeatedly observed a form greatly 

 resembling N. lonijhsima,hwt much smaller and more delicate, 

 varying in length from 0060 mm. to 0'175 mm., while 

 A\ longissima varies from 0'162 to O'lSo mm. The main 

 difference between these two forms consists, however, in the 

 cndochrome, which in xV. /oM^/ss^'wa is composed of numerous 

 elongated bacilliform granules, while in the small form there 

 are two plates, a difference which sliows that they are speci- 

 fically different. This smaller species, which I have named 

 iV. hiplacafa'^, is the same which Van lleurck, not knowing 

 of the difference existing in the endochrome, has mentioned 

 in his treatise on the Diatomacea; (p. 401) simply as a form 

 (forma parva) of iV. longissima. 



In the Pacific 1 have found a variety of N. hiphicata which 

 is smaller and has a much broader girdle-face (fig. 16) ; the 

 latter has a very different appearance from the valve-face 

 (figs. 15, 17). The rostra arc 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 0'0C58-0'01 mm. (usually O'Ol), at the apices 

 0-00:5-00055 mm. 



121. Nitzschiella tenuirostris, Mer. (PI. IV. figs. 1-3.) San 

 Pedro, common. [M.] 



Under the name of N. closterium there have been con- 

 founded a number of forms belonging partly to N. tenui- 

 rostris, partly to another species [N. gracilisj 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, in order to avoid confusion, I aban- 

 doned the old name closterium. Under the name iV. tenui- 

 rostris I understand the following form : — • 



Valve fusiform, abruptly terminating in long very fine 

 rostra, slightly curved on the same side, the whole frustule 

 being arcuate. Striaj and carinal dots invisible. Girdle-face 

 not differing from the valve-face. Endochrome composed of 

 two plates. General length 082-0*180 mm. (usually 



* See my paper on the Diatoms of the Black Sm. 



