CRUSTACEA. 
205 
jointed to the spine itself, and the inner posterior margin articulating with a 
flat thin lamellar spine, which lies in the middle of the membranous 
expansion. 
Dimensions. The single specimen of this species which has been observed 
has the following dimensions; Entire length of carapace (the caudal ex¬ 
pansion being slightlj infolded), 36 mm.; length of cephalothorax, 21 mm.; 
length of basal joints of antennae, as far as visible, 9 mm,; width of caudal 
expansion 17 mm. 
Distribution. In the Erie shales, at Lelloy, Lake county, Ohio. 
