J/ol. XVIII. January, igio. ■ No. 



BIOLOGICAL BULLETIN 



HYDROIDS IN THE ILLINOIS RIVER.^ 



FRANK SMITH. 



During the past summer (1909) while at Havana, 111., in con- 

 nection with the reopening of the Biological Station of the Illinois 

 State Laboratory of Natural History, the writer was surprised to 

 find at one location numerous colonies of a hydroid which pre- 

 sumably belongs to the genus Cordylophora. A superficial 

 examination of the animal and of the literature involved has not 

 disclosed any reason why it may not prove to be C. laaistris 

 Allraan which is a species of hydroid commonly found in brackish 

 water and less frequently in fresh water. 



Numerous colonies were found July 30 in a partially sub- 

 merged willow thicket near the north end of Quiver Lake which 

 is really a part of the Illinois River near Havana. The majority 

 of the colonies were attached to the submerged portions of living 

 willow shoots while a few were found on the leaves and stems 

 of other plants. A later visit was made to the same locality 

 October 16 when the water of the lake was somewhat lowe'r and 

 no longer covered the spot at which the July collections were 

 made. In the part of the thicket which was still submerged, 

 numerous colonies were found attached to dead sticks and 

 branches that projected from the bottom toward the surface. At 

 each visit the collections were made in water less than two feet 

 deep and over which a considerable layer oi Lemna had accumu- 

 lated under the influence of west or northwest winds. In mid- 

 summer the colonies were in dense shade and were associated 

 with a great variety of living organisms among which bryozoans 

 were especially abundant. 



1 Contributions from the Zoological Laboratory, University of Illinois, under the 

 direction of Henry B. Ward, No. 2. 



