^Ir. C. Mercschkowsky on Cali/ornian JJiatoins. 177 



0-120-0-150 mm.), lfi.<,rtl. <.f the body 0-028-0-042 mm., 

 breadth of tlie valve 0-U03-0 OOS mn). 



This 1 consider now as the type species, the var. genuiua, 

 which 1 formerly thought to represent the type, having |)roved 

 to be mueli rarer. 



It is a very delicate, almost metnbranaceous diatom; the 

 rostra aie veiy tine, flexible, usually slightly inflated at the 

 apices; while niuving, the frusUile is constantly turning 

 around its longitudinal axis in the same way as in Cylindro- 

 ihica. The girdle-face does not ditfer from the valve aspect 

 as it does in S^. gracilis, N. bipfacuta, JV. acicularis, N. loii' 

 gissit/iu, <Sic., the rostra being cylindrical, nut flattened as in 

 the above-mentioned species, and the inflated lanceolate part 

 of the frustule or " body " being as distinctly separated from 

 the rostra in tiie valve- as in the girdle-face (compare a and 

 b in flg. 2). A form with straight rostra can be distin- 

 guished from tlie type species as 



Forma directa. (PI. IV. figs. 4, 5.) San Pedro, very comraDn. 



[M.] 



General length 0098-0T6G nun., length of the body 

 0-020-0-038 mm., breadth of the valve 0003-0-0075 mm. 



Although I have occasionally seen such forms in other 

 localities (Black ISea, Villefranche), it is only in California 

 (San Pedro) that I have met with it in great abundance, 

 always, however, in company with the typa. I do not think 

 it advisable to consider such forms as a variety unless they 

 are lound in unmixed assemblages. 



122. Nitzschiella tenuirostris, var. parva, Mer. (PI. IV. 

 tigs. 8-10.) San Pedro, not rare. [M.] 



Differs from the type only by its smaller siz-', being about 

 0*055 mm. in length. 



In my ])aper on the Diatoms of the Black Sea I did not 

 separate tins smaller form from the larger ones which 1 now 

 consider as the type species, and I would not do it even now, 

 preferring to consider the small forms merely as reduced 

 individuals of the type ; but since then 1 have examined a 

 gathering from Theodosia (Crimea) in which this small form 

 is extrentely abundant and in a pertectly pure condition, all 

 the individuals having the same aspect and nuver attaining 

 the size of the type species. This tact compels me (I must 

 confess against my will) to regard it as a distinct variety. 



The same form is not rare in San Pedro, although mi.xed 

 with the larger type species. 



