414 SIR NICHOLAS YERMOLOFF ON SOME INTERMEDIATE FORMS 



is well known and recorded as regards Encyonema Scotica and 

 perhaps Encyonema gracilis, but it does not seem to have b^en 

 noted as regards Cymbella Cesatii. Yet there it is. There is 

 therefore reason to admit that those forms which possess the 

 stigma are iutcr-nediate between Encyonema gracilis and 

 Cymhella Cesatii. Not wishing to multiply names, I have, for 

 convenience' sake, noted such forms with the stigma as 

 Encyonema gracilis-Cesatii. 



(5) The forms which I have sketched and photographed as 

 Cymhella {Encyonema) gracilis-Cesatii in the Herkimer slide may- 

 be a new species. I have nowhere found a correct description of 

 them. Apart from the peculiar stigma they show other peculiar 

 features : their outline is more or less rhomboidal, and on some 

 indi\iduals very cymbelloid, or rather bent along the longitudinal 

 axis. The terminal nodules are always distant. They are very 

 narrow. The stigma gives them a false appearance of Gom- 

 phonema, yet the striae are so radiate that they have not the 

 facies of a Gom/phonema. 



(6) Some of the forms I am about to describe have a decided 

 tendency to triundulate margins, or at least one of the margins 

 shows triundulation. Whether it is a specific characteristic or 

 an intermediate one I cannot say, but anyhow Cymbella angustata 

 is stated by Cleve to be slightly triundulate, and so it is. But 

 slight triundulation is noticeable also in Cymhella Cesatii, the 

 forms sketched as Encyonema gracilis-Cesatii, and also in the 

 robust Encyonema gracilis of the Monmouth-Cherry field deposits. 

 These, however, have nowhere been recorded in existing descrip- 

 tions as regularly triundulate. I am inclined, therefore, to con- 

 sider such triundulation as a sort of transitional characteristic, 

 appearing on intermediate forms. I wonder whether as a rule 

 there may not be characteristics which ought not to be described 

 as "specific," but rather, and only, as "transitional," i.e. as 

 belonging only to intermediate forms. 



(7) As regards hyaline areas (axial and central) these as a rule 

 are more developed on American than on European specimens. 



(8) The majority of forms in the Monmouth-Cherryfield slides, 

 which look very much like Navicula Mi>:imouthiana, nevertheless 

 do Tiot appear to be quite identical with the type form of 

 Navicula Monmouthiana. I will point out the difference at the 



on elusion of my paper. 



