464: Illinois State Laborafoi'y of Natural History. 



Seen from the side (Fig. 6), the shell is highest just 

 posterior to the middle, quickly sloping posteriorly^ 

 more gradually anteriorly. The anterior margin of the^ 

 right valve projects as a hyaline flange, receiving as in 

 a pocket the anterior margin of the left valve, which 

 is armed with a row of eighteen to twenty tuberculiform 

 teeth. Ventral margin slightly sinuate at middle, the an- 

 terior and posterior parts sparsely hairy. 



Seen from above (Fig. 7), the shell is widest back of 

 the middle, blunt and evenly rounded, sides nearly par- 

 allel, then quickly narrowing anteriorly to a rather 

 pointed end. 



Natatory setae of second antennae long, slightly plumose, 

 three of them reaching the entire length of the antennae 

 beyond the terminal claws. Terminal and penultimate 

 segments in female three times as long as wide. 



Mandibles and maxillae not especially marked ; palp 

 of left second maxilla of male as in Fig. 8. 



iMrst pair of feet (Fig. 9) rather stout; terminal claw 

 smooth, much bent, and as long as the last three seg- 

 ments; terminal segment subconical, a third as long as 

 the penultimate, which is of the same length as the an- 

 tepenultimate; latter with a few scattered setae dorsally, 

 and a short, slender seta at the inner apical angle, 

 two thirds as long as the segment. 



Two terminal setae of the second feet (Fig. 10) ap- 

 proximately equal, as long as the last segment, faintly 

 toothed ; terminal segment sinuate on its inner edge, 

 two thirds as wide as long; penultimate segment three 

 and three fourths times as long as the terminal one, 

 four times as long as wide, the dorso-basal edge some- 

 what crenulate, the inner finely ciliate, a plumose seta 

 at its middle point and a comb of cilia at its inner 

 apical angle; antepenultimate segment as long as the 

 penultimate, finely setose on its inner margin and with 

 a rather stout plumose seta at its inner apical angle, 

 as long as the seta on the penultimate segment. The- 



