(18) 



presuppose an acquaintance with the natural history of our crusta.cea, which 

 are as essential to fishes as insects are to birds. 



With a view to removing some of the many difiiculties 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 DEUAPODA. 



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 chelate (3), the first much the largest. 



Gentis Camharus. 



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. 



C acutus, Girard. Areola (6) much wider behind than before. Thorax 

 densely tubcrculate on sides, nearly smooth above. Movable finger much 

 longer than inner side of hand. 



C. tror/lodi/tesi, Leamte. 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, Bundi/. Rostrum broad, short, toothless ; finger not hairy ; 

 first abdominal leg toothed but not recurved at tip. 



