Article X. — Description'^ of New Species of Rotifera and 

 Protozoa from the Illinois Mi/ver and Adjacent Waters. 

 By Adolph Hempei^. 



In April, 1894, the Biological Experiment Station of 

 the University of Illinois was established on the Illinois 

 River at Havana, Illinois. Collections were made from 

 various substations, located upon the river and adja- 

 cent lakes, at stated periods, the intervals varying from 

 one week to one month, Nearlj^ all of the towings made 

 were examined by me, and the list of animals includes 

 ninety species of Rotifera and eighty species of Protozoa. 

 Among the Rotifera there are three presumably hitherto 

 undescribed species of the genus Brachionus. This genus 

 is well represented by ten species and two varieties, and 

 affords an interesting field for study. 



ROTIFERA. 



Brachionus variabilis n. sp. 

 (Plate XXII.. Fig. 1 and 2.) 



This species is remarkable because its posterior spines 

 disappear with age. 



The lorica is smooth and oval in outline. There are 

 six occipital spines, of which the middle pair are longest 

 and are curved outward. The second and third pair 

 are of about equal length, and half as long as the mid- 

 dle pair. There are usually two lateral posterior spines 

 present, which have a slight outward curve. A square 

 plate projects from the dorsal postei-ior edge just over 

 the foot orifice, and is a constant feature. 



The outer pair of occipital spines are strengthened by 

 a sharp spine-like reinforcement at their bases. The 

 pectoral edge is very irregular. There is a sinus in the 

 middle, at each side of which is a papillae-like process. 

 Between these processes and the lateral spines, there is 



