275 



cladia in the same tube, and Schizonema cruciger and the small 

 form mentioned above, both in the same tube, and S. cruciger 

 and Grevillei in the same tube. In all these cases the frus- 

 tules were in lively motion, passing over each other from 

 one end to the other of the tube. In May of the present 

 year, 1869, I found growing in the salt water of the '^ Mill 

 pond " at Salem, Mass., Schizonema cruciger and Nitzschia 

 closterium, W. S. {Ceratoneis closterium, C. G. E., and 

 Nitzschiella closterium, L. R.), both in the same tube. And 

 here it will be necessary to say something in regard to the 

 form I have called Nitzschia closterium, as I shall thereby, 

 I hope, be enabled to clear away a little fog of synonyms. 

 Neither Smithy Kiitzing, nor Rabenhorst describes or figures 

 any species living within a tube like Schizonema, the frus- 

 tules of which have an outline and markings similar to 

 Nitzschia closterium, so that it is not likely that they ever 

 saw anything but the free form or condition of this species. 

 However, Ehrenberg figures and describes, under the de- 

 signation of Schizonema ? Agardhii {Die Infusionsthierchen, 

 1838, p. 343, t. XX, fig. xvi.), a form agreeing with this, 

 but the structure of the frustule is that of Nitzschiella of 

 Rabenhorst, so that the specific name of this species should 

 be Agardhii, whatever its genus be decided to be hereafter. 

 For the present, as it is nearest allied to the forms grouped 

 under Hommcladia, it had better be placed in that genus, so 

 that the synonomy would stand thus : 



Hommcladia Agardhii, C. G. E. (sp.). Abhand. K. Akad. 

 Berlin, p. 311. 1833. 



Ceratoneis closterium, C. G. E. 1840. 



Nitzschia closterium, W. S. 1853. 



Nitzschiella closterium, L. R. 1864. 



What are we to say to such facts as these I record, as 

 well as that of which I sent an account and illustrating 

 specimens to the late Dr. Walker-Arnott, — and which has 

 been noticed by Mr. F. Kitton, who examined my specimens, 

 in Hardwicke's ' Science Gossip ' for May, 1869, vol. v, 

 p. 109, — of the occurrence of what are usually considered 

 two distinct species of Gomphonema, viz., G. capitattmi aiid 

 G. constrictum, both growing upon the same stipes or stalk ! 

 But this is not all. Since then 1 have made gatherings at 

 the same place, and still find the above two forms growing 

 upon the same stalk, and two others of totally different 

 outline which appear also upon the same stipes. So that 

 here we would have four hitherto considered distinct species 

 arising from the same individual. I do not name the two 

 last TTientioned forms, as I am in some doubt with regard to 



