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224 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
FAMILY LYNCEIDE. 
This family, which is numerically the largest among the Cladocera, 
is, in the main, well limited, though there are transitions toward the 
Iyncodaphnide, which are quite direct. The genera Lyncodaphnia, 
Ofryoxus and Ilyocryptus lead toward the Lynceide unmistakably. 
Most of the members of this family are small, comparatively few ex- 
ceeding one millimeter in length. The head is covered with an arched 
shield, which frequently passes with no indentation into the shell of 
the body. This head covering generally extends forward and down- 
ward to form more or less of a sharp angle in front, while in several 
genera it is simply rounded in front. It, in either case, arches over 
the more fleshy lower side of the head from which hang the two short 
antennules and the labrum, while the strong two-branched antennie 
spring from well up under its posterior expansion. The rounded sides 
of this shield, which protect the insertion of the antenne, are called 
the fornices. Above the insertion of antennules is a dark fleck lying 
near or on the lower angle of the brain; this is the larval or nauplius 
eye, which is the first to appear in all these small crustacea. This 
macula nigra is not infrequently as large as the eye itself,* or even 
larger, and in one genus it is the only visual organ. The antennules 
are small and bear on the end several sensory filaments as well as a 
lateral flagellum. The antennules of the male differ very little from 
those of the female. The labrum is furnished with a process, which 
is triangular or semicircular and is usually larger than the terminal 
portion. The mandibles are as in Daphnidw but usually shorter. 
Maxille are often conspicuous, but the first pair of feet serve, by a 
slight alteration at the base, the same purpose. There is rarely an 
indication of the sixth pair of feet, and the antennie have both rami 
three-jointed. The terminal part of the body, or post-abdomen, is 
usually enlarged, and the anal opening is near its base; the armature 
is usually considerable. The form of the post-abdomen is one of the 
best criteria for distinguishing genera and species—a process often 
attended with much difficulty. 
The shell is of various forms, frequently beautifully sculptured. 
The number of eggs produced at one time is limited, and the winter 
eggs are very often laid in the brood-cavity with no preparation of 
the shell previous to it; in other words, the ephippium may be absent. 
On the other hand, sometimes the shell is considerably modified, and 
generally there is a deposit of dark pigment in the upper part of the 
shell. The males are very rare and until recently few were known. 
The diligence of Kurz has added a great many, and we now have a 
* The name “ Lynceus ” is derived from that of the son of Aphareus who was famous for the sharp- 
nameness of his vision. 
f* be 
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