Mr. C. Mereschkowsky on Californian Diatoms. 297 
60. Gyrosigma fasciola (Ehr.), Cl. San Pedro, common. [ M.] 
61, Gyrosigma Febigerii (Grun.), Cl. Laguna near San Pedro 
in nearly marine water, rather common, iC. Mie 
62. Gyrosigma prolongatum, W. Sm. San Pedro, very 
common. [M.] 
I do not see any difference between G. prolongatum and 
var. closterotdes, Grun., the prolongations of the valve being 
turned on opposite sides or on the same side, according to 
the position of the frustule. 
63. Gyrosigma Spencerii, var. exilis, Grun. Laguna near 
San Pedro, very common. [M.] 
64. Gyrosigma tenuissimum, W.Sm. [C.] 
65. Gyrosigma Wansbeckii (Donk.), Cl. Laguna near San 
Pedro, rare. [M.] 
Looks like G. balticum, but the stries are much finer. 
In all the species of Gyrosigma above mentioned which 
I have observed myself, as well as in many others from 
the Mediterranean and the Black Sea, I have invariabl 
found the endochrome to be composed of two plates, while in 
all species of Plewrosigma (with the only exception of P. rigi- 
dum, where it is granular) the endochrome consists of four 
narrow, usually tortuous bands. This proves that Gyrosigms 
and Pleurosigma must be regarded as two natural and 
distinct groups, which should not be united in one genus, as 
has been done by certain diatomists. 
66. Mastogloia (Orthoneis) Wrightii, O’Meara* (nec Cleve). 
(PI.IV. figs. 22,23.) Northern California, notrare. [ M.] 
Valve elliptic, with apices broadly rounded. 
Length: 0-015 0-018 0:020 0:020 0:021 0-028 
Breadth : 0-011 00125 0-014 0-014 0-014 0-020’ 
Median line straight, enclosed between two parallel rows 
of puncta not differing from the rest; axial area linear, 
distinct. Puncta of the valve forming transverse and decus- 
sating rows, the tormer radiate, about 8-9 in 0:01 mm.t; two 
of the median decussating rows more distant, forming a 
double lyie-like figure with both halves uniting at the centre 
with the axial area; marginal rim narrow, with quadrangular 
loculi, 8-9 in 0-01 mm. 
* * Diatomeentafeln zusammengestellt fiir einige Freunde,’ pl. Ixxvii, 
fig. 6. 
+ The engraver did not succeed in representing the great regularity in 
the disposition of the puncta, the poe rows which the latter form 
being therefore invisible in figures 22 and 25 of the Plate, 
