282 A NATURALIST IN THE GREAT LAKES REGION 



Dromogomphus and Gomphus has its sides parallel. Of the two 

 latter the first has acute, spiny-tipped dorsal hooks on the 

 abdominal segments, while in Gomphus such hooks are usually 



FIG. 428. Red-bellied dace, Chrosomus crythrogastcr 



absent and are always dull. Family Cordulegasteridae includes 

 only the genus Cordulegaster. The rest are therefore included 



FIG. 429. Blunt-nosed minnow, Pimephales notatus 



in family Libellulidae, the nymphs of some of which are not 

 sufficiently well known to make accurate determination possible. 

 If there is a pyramidal 

 horn on the front of 

 the head and a small 

 dorsal hook on seg- 

 ment ten, the nymph 

 is of the genus Ma- 



FIG. 430. Johnny darter, Bolcosoma mgrum 



cromia. If the head 



bears a tubercle on each side and segments three to nine bear 



dorsal hooks, the nymph is that of Epicordulia. If the lateral 



