BY THOMAS WHITELEGGE. 501 



Arcella, Ehrenberg. 



A. vulgaris, Ehr. Abh. Akad. Wiss. Berlin, 1830, p. 40, Taf. 1, 

 fig. vi.; Leidy, 170, pi. xxvu. figs. 1, 2, 3, 11, 12, 25, 

 26, 27 and 28. 



Very abundant, almost everywhere, but a very variable species. 

 The numbers of Leidy's figures given above indicate forms similar 

 to those I have observed from many different localities. I have 

 seen forms like figs. 8, 9, 10 and 11 on pi. xxviii. in Leidy's 

 book, from Shea's Creek ; but it is not common. 



A. discoides, Ehr. Monatsb. Ak. Wiss. Berlin, 1843, 139; Leidy, 

 F. Rhiz. N. Amer. 173, figs. 14, 15, 16, 17, 18, 23, 28, 

 30, 31. 



This is perhaps the most common of any ; it is found associated 

 with A. vulgaris and other species in the greatest profusion. 



A. dentata, Ehr. Abh. Akad. Wiss. Berlin, 1830, p. 40 ; Leidy, 

 F. Rhiz. N. Amer. p. 177, pi. xxx. figs. 10-19. 



This very beautiful species is rather rare. I have found it only 

 in two localities, in Shea's Creek and Cook's River. In the latter 

 place I found it on Utricularia ; in the former on the roots of 

 grasses, sedges and floating plants. According to Leidy's figures 

 and description the number of spines is from 9 to 12. The 

 specimens observed by me had from 10 to 15, but their size and 

 general characters are identical with those of European and 

 American examples. The figures given in the " Micrographic 

 Dictionary" and also in Dr. Carpenter's " Microscope and its 

 Revelations/' under the name of A. dentata^ probably represent 

 the var. angulosa of A. vulgaris. 



Centropyxis, Stein. 



C. aculeata, Ehr. Abh. Akad. Wiss. Berlin, 1830, p. 40 ; Leidy, 

 F. Rhiz. N". Amer. 181, pi. xxxi. figs. 1, 3, 4, 12, 14, 23, 



24, 27. 



