528 COSCINODISCUS. 



although the reasons given by Mr. Cox are very plausible, I prefer continuing 

 to separate the Actinocydus from Costinodiscus. In addition, I consider that 

 a seventh" form should be admitted (the Adinocydus having been suppressed), 

 namely, C. excentricus E/ir., which is clearly characterised by its rows of 

 eccentric lines. 



As to the other propositions of Mr. Cox, I frankly admit that they agree 

 somewhat with my own views. Sooner or later it is inevitable that a serious 

 effort must be made to reduce enormously the number of species which are 

 permitted to day. Each further form that is described more or less covers up 

 the differences existing hitherto between certain given species. A time will 

 come, therefore, when it will be necessary to recognize that the number of 

 real species is excessively limited, and the culture method, if that becomes 

 general, will certainly produce material of the greatest value probably even 

 the only such admissible for the definite solution of the difficulty. 



But a single cultivation will not suffice for a given form. These must be 

 prolonged and directed even for a single form in different directions, and 

 it will be necessary to appreciate the influence of different conditions ot 

 existence. My cultivation of phanerograms enables me to advocate this 

 cause, and better, perhaps, than some others. In fact, in my youth, I closely 

 pursued (and that under the direction of Maitre) the cultivations at the Ecole 

 Jordanienne ; I studied with Jordan those innumerable species created at the 

 expense of Draba vema, and many other Linnean forms, and the lessons 

 which I then received have not a little contributed to destroy any illusions, 

 and to give me, with regard to diatoms, ideas similar to those of Messrs. J. D. 

 Cox, Ham, L. Smith, etc. 



But meanwhile, and until sufficient study has enabled us to decide these 

 knotty questions, let us return to the Coscinodiscus of our coasts. I shall give 

 the forms now admissible within reasonable limits. The following table will 

 show that these forms are not very numerous in the limited region adopted 

 for this work : 



