32 Prof. P. T. Cleve and Mr. C. Mereschkowsky on 



simikir in their general appearance, may belong to two quite 

 different species. This may indeed be the case, and we see a 

 beautiful example of it in N. scopulorum ; but in the present 

 instance such a supposition seems to be very improbable. 



Navicula didyma, Ehr. [N. bombus, Ehr.) (p. 62, fig. 66). 



All the four figures belong to Dlploneis didi/ina, but 

 fig. 67, a 1, is certainly not this species. The cell-contents 

 diflfer somewhat from what I have observed in California ; 

 the margins of the plates do not join so closely, leaving a 

 broad space in the middle part of the valve ; they are more 

 finely and regularly indented. Four central ])l£eoplasts of a 

 very peculiar appearance and two libroplasts * are, of course, 

 not mentioned, as Karsten seems to attribute to them no 

 importance whatever. 



Navicula scopulorum, Br^b. (pp. 63, 64). 



The descriptions of the endochrome of this species given 

 by Karsten and myself differ in every respect. There can be 

 no doubt as to the correctness of Karsten's observations, the 

 more so as they fully agree with those of Paul Petit and 

 Brdbisson ; neither can my observations be doubted, as they 

 are corroborated by the var. fascicidata, Gr., which has the 

 same endochrome f. The only possible conclusion is this : 

 there exist two very different diatoms, belonging to two widely 

 separated families (Naviculaceee and Okedeniea?), which are 

 identical as regards the structure of their frustules and valves 

 (see also Nitzschia angularis). 



Navicula (Libellus) constricta, W. Sm, (p. 65). 



Is not the type species, but the var. linearis, Mer.f Does 

 certainly not belong to the genus Navicula, but represents 

 rather a new genus {StauroneUa) . 



Pleurosigma fasciola, W. Sm. (p. 74). 



I have observed hundreds of living specimens of this species 

 in the Mediterranean, in the Pacific Ocean, and in fresh water 

 (California), and I never saw a single individual with four 

 plates. There are always two plates, as in all species of the 

 genus Gyrosigma, s. s. 



Pleurosigma tenuissimum, W. Sm. (pp. 75, 76). 



The above remark applies to this species also : there 



* See for these terms rav paper " Ou Sellaphora," Ann. & Mag. Nat. 

 Hist., Mar. 1902, p. 187. 



t C. Mereschkowsky, " On Okedenia," Ann. & Mag. Nat. Hist. 1901, 

 vol. viii. pi. vii. tigs. 7, 8. 



X C. Mereschkowsky, "On StauroneUa, a new Genus of Diatoms," 

 Ann. & Mag. Nat. Hist. 1901, vol. viii. p. 424. 



