78 TWELFTH ANNUAL REPORT. 



Out of the fourteen genera, two (or perhaps only one) are not 

 yet known from America, while one is restricted to it. The Amer- 

 ican species, 45 per cent of which are new, aggregate 72 per cent 

 of the European. 54 per cent of all the known species are Amer- 

 ican, and most of these have been found within a range of ten miles 

 of Minneapolis. It is probable that the number of species peculiar 

 to America is too high proportionately rather than the reverse, and 

 the comparatively high per cent of new species is due to an actual 

 larger fauna in the New World, Avhile many Old World species 

 remain to be identified. A few of the European species are very 

 likely synonyms, permitting farther reduction. 



This family, which is numerically the largest among the Clado- 

 cera, is, in the main, well limited, though there are transitions to- 

 ward the Lyncodaphnidae, which are quite direct. The genera 

 Lyncodaphnia, Ofryoxus and Ilyocryptus lead toward the Lynceid^ 

 unmistakably. Most of the members of this family are small, com- 

 paratively few exceeding one millimeter in length. The head is 

 covered with an arched shield, which frequently passes with no in- 

 dentation into the shell of the body. This head-covering generally 

 extends forward and downward 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 antenna spring from well up under its 

 posterior expansion. The rounded sides of this shield, which pro- 

 tect the insertion of the antennge, 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 diflfer 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 Daphnidae but usually 

 shorter. Maxillee 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 antennae 

 have both rami three-jointed. The terminal part of the body, or 



* The name "Lynceus"' is derived from that of the son of Aphareus who was famous 

 for the sharpness of his vision. 



