284 REV. E. o'meara. 



Grunow seems to regard tlie distinction of costae and 

 moniliforni strise in this case as founded only on insufficient 

 observation; he says, "The so-called costec in the Pinnularia 

 are quite distinct from the ribs of other genera of Diatomace, 

 and consist of a union of more or less confluent puncta, 

 which, indeed, cannot be clearly discriminated except by the 

 help of good amplification and well-managed illumination/' 

 (' Ueber neue oder ungeniigend bekante Algen. Verhand. 

 der K. H. Zool. Bot. Gesel.,' x B., 1860, p. 513.) Therefore, 

 this eminent author has rejected the distinction between 

 Navicula and Pinnularia, and is followed by Heiberg, Cleve, 

 and others. 



Schuman, who adopts the same view, indicates a peculiarity 

 in some of the larger forms of Pinnularia. P. nobilis and 

 P. major for example which is worthy of special notice, 

 that is, the interposition of very fine strife between the 

 costge, and which are indistinct in N. nobilis, but quite 

 distinct in the case of N. major. These interstitial markings 

 I have never been able to discover and Pfitzer makes the 

 same remark concerning them. The last-named author, in 

 his recently published treatise, ' Untersuchungen iiber Bau 

 undEntwicklungder Bacillariaicen,' maintains the distinctive- 

 ness of the genus Pinnularia, not so much on the grounds on 

 which it has hitherto been based, as on the following pecu- 

 liarities : — 1st. The so-called costae are depressions on the 

 surface of the valve ; ."^ud, the valves themselves are un- 

 symmetrical ; and 3rd, the arrangement of the cell-contents 

 exhibits a marked difference from those of Xavicula, both in 

 the normal condition as also in the process of division. 

 Concerning the characteristics just indicated, a few observa- 

 tions are needful ; as to the first, there is great difficulty in 

 applying it, except in the larger forms. As to the second, 

 this admirable writer is at variance with all preceding 

 authors on the subject, who have regarded the forms in- 

 cluded under the genus Pinnularia as symmetrical. And to 

 me they have ever appeared just as symmetrical as the 

 Navicula. The third character is that which is most worthy 

 of notice, but the forms in Avhicli the peculiarities have as 

 yet been noticed, are comparatively few, so that we must 

 wait for a more complete investigation of the species before 

 we can regard them as satisfactorily established. 



Such is a brief history of the vicissitudes of the genus 

 Pinnularia, so far as I have been able to trace it. For 

 myself, I have been long since disposed to regard the 

 distinction as not quite satisfactory, but inclined at the same 

 time to retain it for the purpose of convenience, inasmuch as 



