p. 7

Crustacea

Astacus
Antennae inserted in nearly the same horizontal line; 6 anterior feet
didactyle; the anterior pair longest; middle division of the
anterior hair longest; middle division of the caudal lamelloe
broader at base; external division biparted
species
Bartonii, Latr. Rostrum mucronate convcave; thorax unarmed; hand
short, destitute of spines; fingers moderate
affinis, Say. Rostrum mucronate, subcanaliculate, 2=spined; a spine
behind each eye, and a large geminate one, on each side
of the thorax; hand + thumb on the inner edge scabrous
Blandingii, Harlan. Rostrum mucronate, [canaliculate], slightly notched at the
extremity; a spine behind each eye; arms tuberculated; fingers unequal
southern states.