74 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
eggs, and is less slender than the adult. The fact that all these species 
are heterogenentic has been frequently reported by the writer. 
Length 1.2 to 1.3mm. Antennal.3 to 1.5 mm. Marsh found the 
species but once, near Marquette. 
* Diaptomus piscine Forbes. 
PLATE V, Fie. 13. 
Forbes ’93. 
A species of medium size (1.75 mm. long), having the last thoracic 
segment not produced but armed with spines. The fifth feet of the 
female has the apical segment of the outer ramus obsolescent and the 
long one-jointed inner ramus provided with spines half as long as the 
ramus. The male feet are very like those of D. leptopus. The outer 
ramus of the left foot has a quadrate basal joint much wider than the 
second segment, which bears a small blunt spine and a long curved 
seta. The inner ramus is nearly as long as both the segments of the 
outer, and terminates in a broadly rounded, or subtruncate, thickly 
ciliate end. The terminal claw of the outer ramus of the right leg is 
short, ciliated; the accessory spine being near its base. The inner 
ramus is longer than the basal joint of the outer, terminating in a 
blunt ciliated end. 
Diaptomus laciniatus Lilljeborg. 
PLATES VILLE Bie. 15° Xs Bre. 12: 
De Guerne and Richard ’89. 
This alpine and northern form may be at once recognized among 
its congeners by the fact that the two last thoracic segments are pro- 
duced on either side into large projections, of which those of the last 
one are enormous and are armed with two minute spines. The first 
abdominal segment is as long as the rest of the abdomen. Caudal 
stylets short. The antenne extend beyond the stylets. Length with- 
out stylets 1.8 mm. to 1.2 mm. 
Diaptomus castor (Jurine.) 
PATH exc mE IG so: 
Jurine ’20 (Monoculus castor); Koch ’35 (Glaucea rubens); Lilljeborg ’53; Lubbock 
65; De Guerne and Richard ’89. 
The confusion of several species under this name and loose de- 
scriptions of European authors stood in the way of any differentiation 
of non-European species until very recently. In fact, until the ap- 
pearance of De Guerne and Richard’s work no writer could feel safe 
in the attempt to distinguish species in this genus, All references to 
D. castor in America are erroneous. In our own ease D. leptopus has 
been most often so called. 
