280 CORRESPONDENCE. 



in Brit. Diat. pt. ii. pi. v. f. 3, has figured a small specimen of this as 

 Nav. dirliynchus E. Again, N. G. AV. Lagerstedt, in his ' Fresh-water 

 Diatomaceae from Spitzbergen and Behring Island,' gives the following 

 list of synonyms, p. 32 : " N. Saxonica Rabenh. — Frustulia Saxonica 

 Eabenh. Bac. Sachs, No. 42 (1851) (see Rabenh. Fl. Eur. Alg. 

 Diat.). Grun. in Rabenh. Beitr. H. ii. p. 10, t. i. f. 13. N. crassi- 

 neriia Breb. in Wm. Sm. Syn. Brit. Diat. v, i. p. 47, p. xxxi. f. 271. 

 Grun. in Wien Verb. 1860, p. 548, t. 3, f. 12." 



But once more. Mr. Hickie has expressed a very high opinion of 

 Schumann's ' Diatomeen der hohen Tatra.' In this remarkable ! work, 



p. 79, I find " Frustulia Saxonica Rabenh Sie tritt in folgendeu 



Formen auf. 1. Nav. crassinervia Breb. Syn. (Brit. Diat.) s. 47, xxxi. 

 271." Dr. Pfitzer, in his * Untersuchen iiber Bau und Entwick- 

 lung der Bacillariaceen,' Bonn, 1871, p. 61, enumerates the particu- 

 lars in which CoUetonema vulrjare and Frustulia Saxonica agree, so that 

 if W. Smith, Brit. Diat. vol. ii. p. 69, is right, we have here another 

 evidence of identity between Navicula crassinervis and Frustulia 

 Saxonica. Sujjpose now we tabulate results, naming only authorities. 



In favour of the identity. Against it. 



Rabenhorst, in 1864. Eabenhorst, 1875. 



De Bre'bisson. 

 A. Grunow. 

 Ralfs, by inference. 

 W. Smith, ditto. 

 Lagerstedt. 

 Schumann. 

 Pfitzer, by inference. 



It is true that Mr. Hickie quotes Mr. Morehouse ; but with all 

 credit to the skill of this gentleman in resolving test-objects, I do not 

 tliink he claims to be an " authority," and I presume knows the 

 diatoms in question only as named by Muller, and other dealers. 



Finally, the genus Frustulia should be abolished ; and I am quite 

 sure that Mr. Kitton, who is, I suppose, at the present time, one of the 

 best, if not the best of English authorities, will agree with me. It 

 was constituted to receive species of Diatomaceae imbedded in amorphous 

 gelatinous substance. I have repeatedly observed CoUetonema vulgare, 

 which in running water is found in tubes, when transferred to quiet 

 water, and exposed to good light, to lose all traces of tubular structure, 

 developing only an amorphous gelatinous mass ; and the little Navicula 

 atomus = Frustulia ijelliculosa is very remarkable in this respect. Mr. 

 Hickie is right in uniting Fi-ustulia (Nav.) Saxonica with Navicula 

 rhomhoides. The latter often occurs in tubes, and De Brebisson's 

 Frustulia (Vanhcurchia) viridula is identical with Navicula rhomhoides, 

 and also with his Nav. crassinervis. I have specimens of all these 

 direct from him, and the difference is too slight to warrant, with our 

 present views as to what is sufficient for such a purpose, the establish- 

 ment of new species ; they merge into each other by almost imjier- 

 ceptible gradation. Everyone who has studied the Diatomaceae, excejit 

 as curiosities, or as test-objects, nay, even in this latter case, is aware 



