296 



will be that already expressed by A. Gleve, viz., that Frag. æqvalis 

 is identical with Frag. capucina. 



Frag. æqv. and Frag. capuc. appear to differ principally in the 

 number of their striæ, but even this difference, if after all any im- 

 portance can be ascribed to it, becomes considerably reduced on 

 further investigation. 



The number of the striæ in Frag. æqv. is given by Heiberg 

 as 20, byLAGERSTEDT (Spitsb., p. 15) as 16 in 10^, while in Frag. 

 capuc, Van Hecrck (1. c.) states it to be 14—15 in \0 fjt. But W. 

 Smith (Syn. II, p. 22) gives the number of the striæ in Frag. capuc. 

 as 40 in 0.001 in., or 16 in 10/^, and Grcnow (Ost. Diat., 1862, 

 p. 366) gives it as 45 — 50 ("und dariiber") in 0.001 in. In case 

 Grunow here was using the Austrian inch, which I have not been 

 able to ascertain, but believe to be probable, this amounts to 17 — 

 19 or more striæ in 16 ^. The Fr'ag. capuc. which I found, had 

 as a rule 17 striæ, but I must add that the striæ, as Heiberg says 

 regarding those of Frag. æqv., are indistinct and therefore difficult 

 to count. I do not doubt, therefore, that Heiberg's Frag. æqv. 

 is merely a variety of Frag. capucina, and this has received further 

 confirmation by my investigation of a gathering which I received 

 on Febr. 12, 1909 from Dr. Henri van Heurck shortly before his 

 death on March 13th of the same year. The gathering comes from 

 Walker-Arnott's coUection and is labelled as follows: "S7S. S. 

 Botanic Garden Copenhagen - Heiberg pr. Eulenstein 1064.'''' In 

 Waleer-Arnott's manuscript catalogue, is found according to van 

 Heurck, the following note upon this gathering: ^'•Fragilaria hidens 

 Heiberg (scarce) also Fr. æqvalis Heib. , Fr. mesolept i Rattr. 

 (very scarce) etc, all var.'s of Frag. capucina.^'' Van Heurck adds 

 in his letter: '■'■Ainsi done W. Am. considerait Frag. æqvalis comme 

 une simple var. du Frag. capucina et W. A. est l'un des tneilleurs 

 connaisseurs de JDiatomées.^'' 



This sample, which contained very little material, but that 

 little particularly well-preserved and very suitable for preparation, 

 showed forms which agree well with Heiberg's figures, but un- 

 questionably belong to Frag. capucina. Fragilaria æqvalis Heib. 

 consequently ought not to be retained as a distinct species. 



ad Tetrac. Lewis, pp. 203—204. 



I am uncertain as to the position of this species in the syste- 

 matic arrangement. It is undoubtedly identical with '-'•Tetracyclus''' 



