150 FRESH-WATER RHIZOPODS OF NORTH AMERICA. 



as in other similar cases, I have suspected to be spores or reproductive 

 germs; though they may not belong to the animal, and may be of parasitic 

 nature. 



Nebela collaris was originally described by me under the name of Nebela 

 numata; but on studying the literature relating to the Fresh-water Rhizo- 

 pods, I have been led to the conclusion that the same had been repeatedly 

 described by Ehrenberg with different names, of which Difflugia collaris is 

 one of the earliest. 



All the forms described and figured by Ehrenberg with the names of 

 Difflugia collaris, D. reticulata, D. cancellata, D. Carpio, D. binodis, D. annulata, 

 D. laxa, and D. ceUulifera, I suspect to pertain to the same animal, and this 

 I suppose to be the same as that I first described as Nebela numata. 



In a systematic arrangement of the Arcellinse,* Ehrenberg has placed 

 the above-named forms, except the last one, in a group he calls Difflugia 

 Beticella. Of this he makes an edentate subgroup, — Allodictya, and a dentate 

 group, — Odontodictya. 



If the names of Beticella, Allodictya, and Odontodictya are to be regarded 

 of generic or subgeneric value, they would apply to the first-named species 

 of the group or subgroups. 



D. Beticella asterophora is the first species of the first subgroup, and D. 

 Beticella binodis that of the second subgroup. The character of the former 

 is obscure; but, judging from the imperfect figure, it is not generically the 

 same as Nebela, and therefore the names of Beticella and Allodictya would 

 not supplant Nebela. Nor would Odontodictya correctly replace Nebela; for, 

 although Difflugia binodis with little doubt refers to what I have considered 

 a variety of Nebela collaris, the term is erroneous, for no species of Nebela 

 is dentated. 



I think it probable that several other forms described and named by 

 Ehrenberg likewise pertain to Nebela collaris, but they are so doubtful that 

 I think it unnecessary to mention them. 



The series of specimens represented by Dr. Wallich in figs. 27 to 33, 

 pi. XVI, of the thirteenth volume of the Annals and Magazine of Natural 

 History for 1864, and described as transition forms of Difflugia symmetrica, 

 appear to me to pertain to the same animal as Nebela collaris. Dr. Wallich 

 remarks that the shell is sometimes compressed, but frequently is not so. 



'Abkand. Akad. Wissens. Berlin, 1871, 244. 



