412 SIR NICHOLAS YERMOLOFF OX SOME INTERMEDIATE FORMS 



Bulnheimii, which is a marine form, whereas all the forms of my 

 study are freshwater. I moreover begin my series with the form 

 which appears to be the ancestral parental one, Navicula Mon- 

 mouthiana. 



The genealogical series which I am about to describe runs in 

 the following order. Here I should like to make the following 

 remark : it is hardly desirable that so-called intermediate forms 

 should receive special names ; it would seem better to give 

 them so-called "hyphenated" nominations, stating the initial 

 form from which they seem to start, and the final form to 

 which they appear to tend. Thus, a form intermediate between 

 Monmouthiana and Stodderi ought to be named thus: Mon- 

 moutJiiana-Stodderi. 



The series runs as follows : 



1. Navicula Monmouthiana Grun. 



2. Navicula MonnioiUhiana Grun. 



3. Navicula Monmouthiana- Stodderi. 



4. Cymhclla Stodderi Cleve. 



5. Cymhella Stodderi Cleve. 



6. Cymhclla aequalis W. Sm. 



7. Cymhella aequalis W. Sm. 



8. Cymhella angustata W. Sm. 



9. Encyonema gracilis Rabh. 



10. Encyonema Scotica W. Sm. 



11. Cymhclla delicatula Kiitz. 



12. Cymhella gracilis-Cesatii. 



13. Cymhclla Cesatii Rabh. 



14. Cymhella microcephala Grun. 



This series could be arranged under one heading which, for the 

 purpose of this paper,! would style the "Monmouthiana Integral "' 

 (Plate 26). 



Although the series begins with Navicula Monmouthiana and 

 ends with Cymhella microcephala, yet I will, in order to follow 

 Cleve, describe the different species in the reverse sequence, be- 

 ginning with Cymhella microcephala. The sketches and micro- 

 photographs accompanying this paper have been taken. from four 

 slides, two from Europe (St. Fiore, Italy, and Premnay Peat, 

 Scotland) and two from North America (Herkimer in the State 

 of New York and Monmouth-Chcrryficld in the State of Maine). 



