(18) 
presuppose an acquaintance with the natural history of our Crustacea, which 
are as essential to fishes as insects are to birds. 
With a view to removing some of the many difficulties which have pre- 
vented a more general study of this captivating and important class, I add 
to the foregoing paper the following simple synopsis of the species men- 
tioned, which it is hoped that any intelligent student may use successfully. 
It is of course a mere compilation designed as a temporary aidto local students. 
A few species from Lake Michigan have been included which have not yet 
been found within the limits of the state, but which must nevertheless occur 
there at least occasionally. 
CLASS CRUSTACEA. 
Arthropoda usually with jointed abdominal appendages and two pairs 
of antennae. All save a few minute forms with more than four pairs of legs. 
Respiration by distinct gills, by gill-feet, or by the general surface of the 
body. 
ORDER DEOAPODA. 
Head and thorax consolidated, forming a cephalo-thorax ; eyes compound, 
on flexible stalks. 
FAMILY ASTACIDAE. 
Abdomen depressed, carapace (1) with a transverse channel, edge united 
with the epistoma (2) ; gills very numerous, composed of filaments ; the three 
front pairs of feet ch e late (3), the first much the largest. 
Genus Cambarus. 
The fifth pair of legs without gills ; last segment of thorax movable. 
Rostrum (4) simple or with one tooth on each side. First abdominal legs of 
male (5) more less divided. 
a 
Oblique tubercle on front margin of third joint of third and fourth pairs 
of legs of male. 
0. acutus , Girard. Areola (6) much wider behind than before. Thorax 
densely tuberculate on sides, nearly smooth above. Movable finger much 
longer than inner side of hand. 
C. troglodytes, Leconte. Areola narrower behind than before. Tho- 
rax granulate on sides, strongly punctate above. Movable claw not longer 
than hand. 
aa 
Oblique tubercle on third joint of third pair of legs of male, none on 
fourth pair. 
b 
First abdominal legs of male not distinctly bifid. 
C. gracilis, Bundy. Rostrum broad, short, toothless ; finger not hairy ; 
first abdominal leg toothed but not recurved at tip. 
