482 Mr. C. Mereschkowsky on 



large, smooth, with almost parallel internal margins ; marginal 

 striae 11 in 001 mm., axial striee 13-14 in O'Ol mm. Puncta 

 indistinct. 



Among the numerous varieties of this species enumerated 

 by Cleve * there is not a single one which is described as 

 having valves with rostrate ends. I think therefore that the 

 above-described form belongs to a new variety. From its 

 small size it might be referred to the varietas minuta, CI. 

 (size, according to Cleve, 0*027-0*05 mm.), or the varietas 

 tahitensis, CI. (size 0'G4-0"045 mm.) ; but as Cleve does 

 not give in his ' Synopsis of the Naviculoid Diatoms ' a suffi- 

 cient description of these two varieties and I do not possess 

 his work ' On New and Hare Diatoms,' where they are 

 figured, it is impossible for me to ascertain whether it is so 

 or not. It seems, however, not very probable that this 

 form belongs to the first variety on account of the striae, which 

 are here 11 in O'Ol mm., while in the varietas minuta they are 

 8-10 in 0"01 mm. The same reason makes it even more 

 improbable that the above-described variety belongs to the 

 varietas tahitensis, which has 13-14 marginal stria3. From 

 Tahiti I know another variety of Navicula Hennedyi, the 

 valves of which have also subrostrated apices ; but this latter 

 (PI. XVI. fig. 15) differs from the varietas subrostrata in the 

 lateral areas, which are of a somewhat different shape, their 

 interior margins being divergent; the ends of the valve are 

 also more or less elevated. I will give the description of the 

 variety from Tahiti in a future note on Polynesian Diatoms ; 

 I give here the figure of the latter in order to make the com- 

 parison of both forms easier. 



3. Trachyneis aspera, Ehr. Rather rare. 



4. Plenrosigma nicobaricum, Grun. Rare. 



Cleve, in his ' Synopsis of the Naviculoid Diatoms' f, attri- 

 butes to this species a length of 0T4 mm. I have seen a 

 specimen attaining 0"267 mm. in length, with a breadth of 

 0'036mm., not differing in other respects from the description 

 which Cleve gives of this species. 



5. Cocconeis costata, var. pacifica, Grun. Very rare. 



6. Cocconeis scutellum, Ehr. Rather rare. 



* Cleve, ' Synopsis of the Naviculoid Diatoms/ part ii. p. 58. 

 t L. c, part i. p. 36, 



