95 
fish (Forbes, ’80) such as the Catostomide and some of the Silu- 
rid@é and minnows. I have found them in great abundance in the 
intestine of the adult gizzard-shad (Dorosoma), and in the contents 
of the digestive tract of the German carp (Cyprinus carpio). 
In the pages which follow, the seasonal distribution, or occur- 
rence in the plankton, of thirty-one R/izopoda is discussed, and 
the presence in the plankton of the Illinois of twenty-eight other 
rhizopodan forms which have been recognized by other writers as 
of specific rank is noted. This by no means exhausts the rhizopo- 
dan fauna of the environment which was the field of this investiga- 
tion. A continued study of the plankton itself would doubtless 
greatly extend the list of adventitious forms from the shore and 
bottom, and a more careful analysis of the variants, especially in 
the Difflugia globulosa-lobostoma group, would still further increase 
the richness of the fauna from the systematic point of view. Hem- 
pel (99) lists sixteen species from this locality, and Penard (’02), 
in discussion, remarks: ‘Une pareille pauvreté dans une région 
riche en organismes de toute nature, est une impossibilitié maté- 
rielle.”” However, neither Hempel’s paper nor the present one 
pretends to give a full account of all the Riizopoda of the region. 
He dealt largely with plankten collections, and the present paper 
deals with them exclusively. 
There is but little in plankton literature which gives with any 
fulness the seasonal distribution of the Khizopoda,or indicates that 
they are of any considerable importance in the economy of the 
plankton. The importance which they acquired in the plankton of 
the Illinois is no doubt in part due to the nature of the environ- 
ment with which we are dealing. The somewhat sporadic and 
meteoric character of their appearances in our waters leads to the 
inference that full seasonal analyses of the plankton of other bodies 
of water at brief intervals may reveal a greater prevalence of the 
Riuzopoda in the plankton than has hitherto been detected. 
DISCUSSION OF SPECIES OF RHIZOPODA. 
Ameba limax Duj.—This was frequently abundant in the water- 
bloom of midsummer, but was not identified in the plankton 
collections. 
Ameba proteus Résel.—Average number, 342. The individuals 
here assigned to A. proteus include those taken in our plank- 
