HOW TO KNOW THE IMMATURE INSECTS 



ORDER EPHEMEROPTERA 



la. Thorax shield-like covering most abdominal segments; gills in- 

 visible. Fig. 131 Family PROSOPISTOMATIDAE 



The naiads ore flat and disk-like. The gills are 

 concealed by a large shield-like thorax. Their three 

 caudal filaments are short. They live in swift running 

 water, and are vegetable feeders. It belongs to the 

 old world. 



Fig. 131. Pro- 

 sopistoma folia- 

 ceum Fourcroy. 



lb. Thorax not shield-like; gills visible 2 



2a. Mandibles extending anteriorly far beyond the head; gills plu- 

 mose • 3 



2b. Mandibles short; gills not plumose 6 



3a. The projecting part of mandible shorter than head; gills extend- 

 ing laterally. Fig. 132 Family POTAMANTHIDAE 



The naiads live upon silt-covered stones and 

 muddy bottoms. The mandibles are tusk-like 

 but short. The gills are long and plumose. They 

 feed on the vegetation of their area. 



Potaman- 



3b. The projecting part of mandible almost as long as head; gills ex- 

 tending dorsally 4 



62 



