132 THOMAS SAY FOUNDATION 
PLATE 4 
FIGURES 50-65 
50-54 Perla bilobata Ndm. and Cisn. 
Note the unique structure of the maxilla. The galea is reduced 
to a very small appendage and the lacinia is smooth and uniden- 
tate. 
55-59 Perla verticalis Banks 
Mouth parts similar to those of the above species but the galea is 
a little longer and the lacinia is bidentate and possesses a few 
hairs. 
60-65 Perlesta placida Hagen 
The submentum of the labium is short and wide; the second 
tooth of the lacinia is followed by a single hair. 
