EEPOET ON THE DIATOMACE.E. 35 



Navicula, sp. (?) (Plate XXVII. figs. 3 and 7.) 



We have here delineated two other navicular forms, both being represented in their 

 zonal aspects, probably owing to the fact that they possess very narrow valves. Both 

 possess a similar striation, but while the profile in fig. 3 is curvilinear, that in fig. 7 

 is straight. This difference may be explained by saying that in fig. 3 the zonal side is 

 seen somewhat obliquely. 



The perfect resemblance of the striation and the identity of their locality — both being 

 found to the south of Heard Island — render it very probable that both forms represent 

 the same species, or at most that one is a variety of the other. 



Although the minute transverse striation might point to an identity between these 

 forms and Navicula liber, 1 Sm., such an opinion, on closer examination, cannot be enter- 

 tained, the striation, which is characteristic of the connecting zones in the present frustules, 

 differing from the corresponding sculpturing in Smith's species. 



Navicula, sp. (?) (Plate XXVII. fig. 10.) 



This figure represents a single valve which must belong to another species of Navicula. 

 Its general outline is plano-convex, and its extremities well defined and bluntly recurved. 

 The longitudinal axis exceeds two and a half millimetres in length. It is transversely 

 granulated, save in the narrow areola which surrounds the central nodule. The probability 

 that this is a sporangial frustule may be borne in mind. 



No navicular form hitherto recorded possesses so large a size as the present one, whose 

 specific designation must, however, remain undecided till further observations have been 

 made. 



Alloioneis, Schumann. 



The late Professor Schumann, recognising the advisability of separating from the 

 extensive genus Navicula all those forms that possess distinctive characters in common, 

 established the genus Alloioneis for frustules which, while they were symmetrical in their 

 external profile, had long strise on one side of the raphe and short on the other. 



This new genus, which has been accepted, amongst others, by the Swedish micrographer 

 Professor P. T. Cleve, has been defined by Schumann 2 as follows : — " Navicula, ab altera 

 linese longitudinalis parte pinnulis longis, ab altera parte pinnulis brevibus prsedita, sectione 

 transversa rhomboidea." 



Alloioneis antillarum, CI. et Grun., var. no v. (Plate XV. fig. 5 ; Plate XX. fig. 1 4 ; 

 Plate XXVIII. fig. 14.) 



Plate XX. fig. 14, represents a diatom which resembles the species established by 

 Cleve under the name of Alloioneis antillarum, CI. et Grun. 3 It may be noted, however, 



1 Smith, op. cit, vol. i. p. 4S, pi. xvi. fig. 133. 2 Die Diat. d. H. Tatra, p. 73, 1867. 



3 Diatoms from the West Indian Archipelago, hy P. T. Cleve, p. 8, pi. i. fig. 11, 1878, published in Bihang 

 k. Svenska Vet. Akad. Handl, Band V., No. 8. 



