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IV. — Bemarks on Frustidia Saxoniea^ Navicula rhomboides, and 



Navicula crassinervis. By Charles Stodder, U.S.A. 



{Read he/ore the Eoyal Microscopical Society, May 3, 187G.) 



As there seems to be much uncertainty prevaiHng in regard to the 

 three species named above, I will attempt to clear the matter up. 

 To do this it is needful to refer to the original descriptions, aided 

 by the light of the most recent classification. Ealfs — Pritchard's 

 'Infusoria,' p. 924, 1862 — gives the generic character of Frustulia 

 (Ag.), " Bacillar immersed in an amorphous gelatinous substance ; " 

 F. torfacea (Braun), " Rhomboid lanceolate, with obtuse apices, 

 stout median rib, and small central nodule ; " F. Saxonica, " Slen- 

 derer than F. torfacea, valves more acute, front view linear, with 

 broadly rounded ends." These are unquestionably the original 

 descriptions of the authors. But Professor H. L. Smith (than 

 whom there is no better living authority), " Conspectus of the 

 Families and Genera of the Diatomaceae," ' The Lens,' Chicago, 

 1872, rejects as a generic distinction the mode of growth, and con- 

 sequently the whole genns Frustulia. Except the mode of growth 

 there is no one character or combination of characters to distin- 

 guish Frustulia from Navicula. Mr. Hickie, this Journal, p. 127, 

 No. Ixxxvii., confesses " that he is unable to state where Frustulia 

 Saxonica ends and our small rhomboides begins." In this he only 

 confirms what diatomists have known for the last ten years. Now 

 what is N. crass. ? Wm. Smith, ' British Diatomaceae,' 1 852, gives 

 N. 'crassinervia Breb., " Valve elliptic lanceolate, extremities pro- 

 duced, striae obscure, length • 0013" to •0026"." N. rhomhoides, 

 Ehr., "V. nearly quadrangular, striae very faint parallel, "85" 

 to • 001"." * There is nothing to distinguish one from the other, 

 except the produced extremities of N. crass. Now that is such a 

 trivial distinction, so far within all known and all but universally 

 acknowledged variations of other species, that probably no student of 

 these plants would at this time make use of it as a specific character. 

 But this is not all; Prof. H. L. Smith now owns all of De 

 Brebisson's material. Since this discussion commenced Prof. S. 

 has sent to me prepared from that material a slide of " Nav. rhom- 

 hoides,'' and one of " N. crassinervia," with the comment that he 

 could " see no difi'erence between them." After a careful study of 

 both slides I fully concur with Prof. Smith's conclusion. Neither 

 Dr. Woodward's 'photographs nor the lithograph copy of Seibert's 

 photograph show any specific distinction. 



* Navicula rhomhoides in all its varieties is found throughout New England, 

 but its head-qiiartcfs seem to be in the little ponds and streams among the white 

 mountains of New Hampshire. There is one deposit on the bottom of Benin's Lake 

 (see Lewis, in 'Proc. Philii. Acad. Nat. Sciences,' 1865), every slide of which will 

 contain hundreds of frustules of all sizes. I have measured them fiom •0007" 

 to •0017", varying in closeness of striation nearly in proportion to the size. Of 

 course, as I consider the three names belong to Imt one species, I must believe 

 that all of them will show longitudinal striation. 



