186 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
22 Spine moderate, springing from the middle of 
the caudal margin. . . .. . . . arcuata, 190 
tt Head uncrested. 
@ Spine short or absent. 
|| Abdominal process united at the base. . gibbosa, 191 
|||| Abdominal processes discrete. 
{ Spine near the middle of the caudal margin. 
° Anal teeth 20 to22. . .:. ... . Ovata, 19% 
9° "Anal teeth 9 to 10... .+%. 52... =>, QObiusa, ie 
{| Spine at the dorsal angle. So ae ea pina, 192 
2% Spine of considerable length. 
|| Spine near the middle of the caudal margin. 
| Ventral margin of the head convex. . hastata, 192 
{| Ventral margin of head concave. 
° Eye distant from the margin of the 
heaa? 5: ee tees: ie ee ORMED bare lo 
°° Eye near the margin of the head. 
x Abdominal processes united at the 
base. soe Se 5 Sehoedieriiass 
xx Abdominal processes discrete. brevispina, 193 
\||| Spine nearer the dorsalangle. . . . . pulex, 193 
** Claws of the post-abdomen without a basal comb of teeth. 
+ Antennal sete thick, first segment longer than the second. 
{ Spine near the middle of the caudal margin. ventricosa, 195. 
tt Spine above the middle of the caudal margin. . caudata, 195 
+t Antennal setz with the second segment longer than the first. 
{ Headhelmeted. = 6)C25° 6 Poe, ss 2 eV 
tt Head not helmeted. 
2 Abdominal processes united. 
|| Dorsal margin strongly carinate. . . . . Sarsii, 198 
\\\| Dorsal margin slightly or not carinate. 
‘| First abdominal process much the longer. 
° A deep depression separating head and 
body. © oss. ats) (paludicolasies 
°° Avery slight depression separating head 
and body. longispina,199; minnesotensis,199 
{ Abdominal processes nearly equal. 
oul 
° Anal claws 12 to22. . . . . cGavifrons, 200 
°° Anal claws 7 to 23. . . . microcephala, 200 
22, Abdominal processes discrete. 
|| Abdominal processes short, equal. . . . rosea, 20 
|||| First abdominal process twice as long as the second. ; 
Beak not greatly produced ventrad. . aquilina, 200 
{{ Beak greatly produced ventrad. . . lacustris, 201 
tit Head with a dorsal toothed crest. 
2 Crest just in frontofthe heart. . . . . dentata, 201 
22 Crest over the bases ofthe antenne. . . dentifera, 202 
II. Pigment spot absent. 
A. Head not helmeted or but slightlyso. . . . . . . longiremis, 202 
B. Head helmeted. 
