186 GEOL. AND NAT, HIST. SURVEY OF MINNESOTA. 



§§ Spine moderate, springing from the middle of 



the caudal margin arcuata, 190 



II Head uncrested. 



I Spine short or absent. 



II Abdominal process united at the base. . gibbosa, 191 

 nil Abdominal processes discrete. 



^ Spine near the middle of the caudal margin. 



° Anal teeth 20 to 22 ovata, 191 



°° Anal teeth 9 to 10 obtlisa, 191 



If^ Spine at the dorsal angle alpina, 192^ 



§§ Spine of considerable length. 



II Spine near the middle of the caudal margin. 



1[ Ventral margin of the head convex. . liastata, 192^ 

 T[l[ Ventral margin of head concave. 



° Eye distant from the margin of the 



head oriiata, 192^ 



°° Eye near the margin of the head. 

 X Abdominal processes united at the 



base sclioedleri, 193 



XX Abdominal processes discrete, brevispiua, 193 



III! Spine nearer the dorsal angle pillex, 193 



** Claws of the post-abdomen without a basal comb of teeth. 



t Antennal setie thick, first segment longer than the second. 



J Spine near the middle of the caudal margin. ventricosa, 195 

 XX Spine above the middle of the caudal margin. . caudata, 195 

 ft Antennal setaj with the second segment longer than the first. 



X Head helmeted hyaliua, 195 



XX Head not helmeted. 



I Abdominal processes united. 



II Dorsal margin strongly carinate sarsii, 198 



nil Dorsal margin slightly or not carinate. 



T[ First abdominal process much the longer. 

 ° A deep depression separating head and 



body paludicola, 198 



°° Avery slight depression separating head 



and body. loiigispina,199; imnnesotensis,199 

 T[^ Abdominal processes nearly equal. 



° Anal claws 12 to 22 cavifrons, 200 



°° Anal claws 7 to 23. . . . niicrocephala, 20O 

 §§ Abdominal processes discrete. 



II Abdominal processes short, equal. . . . rosea, 200 

 nil First abdominal process twice as long as the second. 



^ Beak not greatly produced ventrad. . aqiiilina, 20O 

 T[1[ Beak greatly produced ventrad. . . lacustris, 201 

 XXt Head with a dorsal toothed crest. 



? Crest just in front of the heart dentata, 201 



§§ Crest over the bases of the antennte. . . dentifera, 202 



II. Pigment spot absent. 



A. Head not helmeted or but slightly so longiremis, 202 



B. Head helmeted. 



