105 



Corisa aUernata, Say. 



(Joiir. Acad. Nat. Sci. Phil., N. Ser., iv, 329, 1825; Compl. 

 Writ., ii, 251.) 



This is the commonest Illinois Corisa. It was less abundant in 

 some of the Quincy pools than the preceding, but was more 

 widely distributed. Noted especially in Cedar Creek and Long 

 Lake. The eggs are oval and have a small prominence at the 

 free extreinity. They are attached generally to plants. 



ORDEK ORTHOPTERA. (Crickets and Grasshoppers.) 



This is a strictly terrestrial group, and calls for mention here 

 only because of the constant presence, on the banks of streams 

 and pools, of species belonging to it, which doubtless have an ef- 

 fect as fish-food, and otherwise, on aquatic life. At Quincy, a 

 small cricket {Tridadylus apicalis) occurred in myriads among 

 weeds which were springing up from the mud at the edges of 

 sloughs, and individuals were sometimes found upon the water. 



ORDER PLECOPTERA. 



Wings four, membranous, net-veined, sometimes folded longi- 

 tudinally when at rest. Antennae long and setiform. Tarsi 

 3-jointed. Prothorax wide. Abdomen frequently with two long, 

 jointed caudal stylets. Larv® and pupee like the adults excepting 

 as to size and wings. 



Small insects, which, as nymphs, live under rocks and boards, often 

 in swift-flowing water. The pupa takes food, and after attaining 

 its growth leaves the water and transforms to the winged adult. 

 In a number of points they are allied to the grasshoppers. 



Plecopfera, nymph. 



A flat nymph found in Willow Slough. It is about .52 inch long 

 and bears at the end of the abdomen two long, jointed appendages. 

 The antennae are long and slender, the mouth parts much like 

 those of a grasshopper or cockroach. Head very wide, and with a 

 pair of compound and three simple eyes. Three divisions of the 

 thorax large, with expanded tei-ga, and bearing at each side 

 cottony respiratory tufts. Legs with strong femora and three- 

 jointed tarsi. 



They were not common at Quincy, probably because the waters 

 do not furnish them suitable shelter. 



ORDER ODONATA. (Dragon Flies, Snake Feeders.) 



With four large membranous, net- veined wings. Mouth provided 

 with strong biting mandibles. Antennte minute. With compound 

 eyes. Prothorax very small. Tarsi of three articles. Abdomen 

 with caudal appendages. The pupte are active and aquatic. The 



