140 KITTON, ON DIATOMACE^. 



suppose the crenulations represent the undulations of the 

 alse, and that the margin of the valve is not shown in the 

 figure. 



Mr. Roper, at page 17, vol. viii, of this .Journal {Campy - 

 lodiscus productus), says : " The markings and canaliculi on 

 most species of Surirella are subject to considerable varia- 

 tion, and afford no good grounds for specific distinction." 

 Professor W. L. Smith, who has long studied the habits of 

 living diatoms (quoted by Dr. Lewis in his valuable paper 

 on " Extreme and Exceptional Variations of Diatoms"), says : 

 *' When I find Navicula amphirynchus congregating, and 

 producing Navicula ferma, Stauroneis gracilis producing 

 S. PhcBnieenteron, and Surirella splendida S. nobilis, quite 

 different in form and striation, I cannot but doubt the 

 propriety of making new species out of every different form 



AND MARKING. '^ 



Eupodiscus excentricus I still refer to Coscinodiscus 

 minor* of Kutzing (not of the synopsis), and, after a careful 

 examination of many specimens from various localities, I 

 find the excentric areolation precisely as figured by the Rev. 

 E. O'Meara, and in he majority of cases a circle of obtuse 

 spines may be easily seen. I do not, however, find any 

 with what I suppose to be an abnormal marginal development, 

 as shown in E. excentricus. 



The Rev. E. O'Meara says, that a careful consideration of 

 the figures and descriptions of Raphoneis Jonesii and R. 

 Moorii would convince that Mr. Kitten's opinion, that they 

 are identical, is untenable. '' The sculpture in the tAvo forms 

 exhibits a greater diversity in structure than is considered 

 sufficient in other forms to mark diversity of species." I 

 have carefully compared the figures, and to me the sculptur- 

 ing seems to be precisely the same in both forms ; take away 

 the margin, and it would be impossible to distinguish one 

 from the other. I saw that the description did not accord 

 perfectly with the figure, but as it was nowhere stated that 

 the figure was erroneous, I had no means of knowing which 

 was correct. The suggestion that Raphoneis Archerii might 

 be the upper valve of Cocconeis clavigera is not so difficult 

 to comprehend when the structure of the genus Cocconeis is 

 understood ; the difference between Raphoneis Archerii and 

 Cocconeis clavigera is not greater than that between the 

 upper and lower valves of Cocconeis Grevilli. 



Stauroneis rhombica, n. sp., O'M., appears to resemble 

 Stauroneis apiculata of D. Greville (in ' Edinburgh New 



* This may possibly be the small form of C. excentricus figured in the 

 ' Synopsis.' 



