376 Illinois State Laboratory of Natural History. 



except the two shallower lakes, Phelps and Flag. It was 

 present from April to November, and was most common dur- 

 ing the period from July to September. 



69. M. quadridentata Ehrbg. 



This was found at all of the substations except that in 

 Phelps Lake. It occurred from May to December and was 

 uniformly present, though never very abundant, throughout 

 the warmer months, from June to October. 



70. M. closterocerca Schmarda. 



Scattered occurrences at various times and places char- 

 acterize the record of this rather rare species. A maximum 

 in September is feebly indicated. It was found in all the 

 deeper lakes. 



71. M. mollis GossE. 



Kare, being taken only in towiugs from the Illinois River 

 in August. 



Family COLURIDiE. 



COLURUS Ehrbg. 



Body subglobose, more or less compressed ; lorica com- 

 posed of two lateral plates, open in front, united dorsally, 

 gaping behind, and generally open ventrally ; frontal hood in 

 the form of a hook, not retractile ; foot permanently extended ; 

 of distinct joints, terminated by two furcate toes. 



72. C. deflexus Ehrbg. 



Occurred only in oblique towings from Quiver Lake, during 

 March. 



73. C. bicuspidatus Ehrbg. 



This species was not common at any time, and was found 

 only in the Illinois River and deeper lakes. It was present 

 from July to October, also once in April, frequenting l»oth 

 vegetation and open water. 



74. C. obtusus GossE. 



This attractive minute species was found in Quiver Lake 

 and once in the Illinois River. It w^as taken among vegeta- 

 tion and in towings from June to September. 



