296 THE AMERICAN NATURALIST.  [Vor. XXXIV. 
A 
& 
c. Lateral parts of head scarcely expanded. Eyes, when present, 
small, lateral. Peduncle of inferior antenne without small 
accessory appendage outside of third joint. Legs ambulatory, 
except first pair, which are distinctly subcheliform ; legs with 
dactylus generally uniunguiculate. First pair of pleopoda in 
female very small, not operculiform. Outer lamella of second 
pair very large and incrusted, so as to form, together with 
the corresponding lamelle of the other side, a sort of oper- 
culum, covering the two succeeding pairs. 
Family XV. Asellidz 
c. Lateral parts of head lamellarly expanded. Eyes, when present, 
usually subdorsal. Peduncle of inferior antenne generally 
with small accessory appendage outside of third joint. Legs 
ambulatory, except first pair, which are sometimes prehensile ; 
legs with dactylus generally bi- or tri-unguiculate. First pair 
of pleopoda in female transformed into a single, large oper- 
culum. Outer lamellz of two aca pairs narrow and 
confluent with basal part . . Family XVI. Janiride 
&. Three posterior segments of it, ‘as a rule, sharply marked off 
from four anterior ones, and much smaller. Caudal segment 
more or less vaulted above, subpyriform. Eyes, when present, 
placed on the tips of lateral peduncle-like projections of the head. 
Superior antennæ placed widely apart. First pair of legs much 
shorter than others. Succeeding pairs more or less rapidly 
increasing in length . . Family XVII. Munnidæ 
Eyes wanting. First pair of S bdbicbbesstté: Last three pairs of 
legs natatory, with some joints flattened and ciliated. First pair of 
legs shorter than three following pairs. Second, third, and fourth 
pairs very elongate . . . . . . Family XVIII. Munnopside 
FAMILY XV. ASELLIDH (FRESH-WATER ISOPODA). 
Mandibles without a palp. Last six pairs of = with dactylus biun- 
guiculate Mancasellus Harger 
Mandibles wits a dives: jobohed potis Lari six t pue of ad uniunguicu- 
ate. 
5. Eyes present. Body oblong, depressed. Head seca narrower and 
shorter than first thoracic rar Caudal segment not longer 
than broad . . . Asellus Geoffroy 
F. Eyes wanting. Body dong, ul narrow. Head large, not narrower 
than first thoracic segment, and longer. Caudal segment much 
longer than broad . . . . o . Ceeidotea Packard 
Genus Mancasellus Harger. 
a. 
Lateral margins of head entire. : 
Mancasellus brachyurus Harger, Virginia 
