478 J!iJr. C. Meiesclikowsky on CuUfomian Diatoms. 



A Ptill smaller form, 0*035-040 mm. in length, with very 

 short rostra, can be distinguished as 



Forma minutissima. (PI. IV. fig. 11.) San Pedro, rather 

 rare. [.M.] 

 The forma semicircularis and variefas arena, Mer. (the 

 latter attaining 0*364 mm. in length), belonging to the same 

 proup, are mentioned in my pa|ier on the Diatoms of the 

 Black Sea. 1 have not seen thorn in the Pacific. 



123. Nitzscliiella tenuirostria, var. hamulifera, Mcr. {N. fenui- 

 rostn's^ var. (jenuina, Mer. Diat. lihick Sea). (PI. IV. 

 figs. 6, 7.) Sun Pedro, rare. [M.] 



Diflers by the very thin elongated rostra, which are straight, 

 becoming curved and spirally twisted at the apices only, 

 where they form a hook. General length 0*140-0"104 mm., 

 length of the body 0045 mm., breadth of the valve 0*006 mm. 



This variety is very frequent in some localities of the 

 Black Sea. I have found it also in the Mediterranean (Ville- 

 franche). The hooks are not always so distinct as re[)re- 

 sented in lig. G. 



124. Nitzscliiella gracilis, Mcr. (PI. IV. figs. 12, 13.) San 

 Pedro, rare. [M.] 



This is quite a distinct species, differing from JV. tenui- 

 rosfris by the more robust frustule, the rostra being broader, 

 straight, curved in the same direction at the ends only ; they 

 are flaitened, especially at the aj)ices, which makes them 

 appear broader and more hyaline at the girdle-face. Endo- 

 chrome composed of two plates. While moving, the frustiilj 

 does not turn around its I'jngitudinal axis. Length 0*126- 

 0'165 mm., attaining 0245 mm., breadth of the valve 00052- 

 0-008 mm. 



125. Nitzscliiella gracilis_, var. reversa, Mer. (PL IV. fig. 14.) 

 San Pedro, very common. [M.] 



Rostra curved in opposite direction.^. General length 

 1-0*175 mm., length oi the body about 005 mm. bi*eadth 

 of the valve 0'008-00o9 mm. Very common in San Pedro, 

 where the type species is very rare ; the opposite is the case 

 iji VdKfraiich<' (Mediterranean) and the black Sea. Var, 

 reversa is also frefjf.ent in fresh water, (Jalilbrnia (Los 

 Angeles). 



The following table will facilitate the distinction between 



