186 THE AMERICAN MONTHLY [An-nst, 



this subject was not accessible to me ; and as many of the forms 

 were unfamiHar, and the reports of many experts to whom they 

 were submitted were so incompatible, I did not like to pro- 

 nounce upon them myself. I found what appeared to be an ob- 

 stinate determination on the part of some not to admit the possi- 

 bility of any new discovery, and an equally determined opposition 

 to any revision of existing genera. This seems to me as un- 

 reasonable as it will be futile, particularly as regards the Naviciila ; 

 for even if Prof. P. T. Cleve's new revision is not accepted in full, 

 some other must be soon. Many valued correspondents write me 

 that they fear that the separation of the Navicula into new^ genera 

 and species will result in confusion, and complicate the study. 

 Precisely the opposite effect may be expected, for if the new 

 genera have obvious characteristics, the study and the determina- 

 tion of unfamiliar forms will be greatly simpliHed. 



In his introduction to his recent " Monograph of the Genus 

 Pleiu'osig-ma" Peragallo remarks: " The genus being well de- 

 fined remained in spite of the opposition of Ehrenberg. That 

 stupefying micrographer, who on his own part multiplied beyond 

 all measure the genera and species upon the most frivolous charac- 

 teristics, not only would never admit the genus of vSmith, but 

 also united almost all its species under the name of Navicula 

 sii^ma." It is not likely that the present opposition to revision 

 will be any more effective than that of Ehrenberg. Feeling satis- 

 fied that the varieties in question had been previously undescribed, 

 I sent slides to some of the most eminent specialists of Europe. 

 They reported all the forms 7ieiv^ that they had been named and 

 would be described and illustrated in monographs of different 

 genera soon to be published. Three of the Pleurosigma of Mor- 

 ris creek appear in H. Peragallo's excellent "Monograph" 

 published in late numbers of Le Diatomiste. The description 

 is as follows : 



Plcjirosigina Terryatium. H. P. (Balticum var .f*) . 



In a very fine collection of Mr. Terry coming from marsh, 

 South End (Connecticut), and which will be published in the 

 series Tempere and Peragallo, is found very frequently a form 

 which has the general appearance of the strigitis and the striation 

 of tlie Balticum. 15.5 stria in 10 u. Length 0.400-0.450, width 

 0.03S-0.041. PI. vii, f. 31. 



Pleurosigma decorum. Sm. (var.'') Americanum, H. P. 



Larger than the type, raphe less eccentric, striation according to 

 type, silica more delicate. Dike creek. W. A. Terrv. PI. 



i,f.9- . 



Ple7irosigma paradoxum. tl. P. 



A little smaller and less finely striated than the preceding 

 (^P. culinaritm Grun). Striae oblique 20-21, transverse 1S-19. 



The latter less visible though more separated than the oblique. 

 Numerous measurements leave me no doul)t upon this point. 

 Abundant in a gathering from Morris creek by Mr. Terry. PI. v, 

 f. 13. 



