STATE GEOLOGIST. 67 



again included with the Daphnid^, The writer, upon the dis- 

 covery of the Lyncodaphnia, was forced to regard this group as of 

 €quivalent grade with the above mentioned families and again pro- 

 posed the family name Lyncodaphnidse. ^ 



The genus Ilyocryptus is a little one side the normal course of 

 the family and seems related to the lynceid genus Leydigia. 



The waters of the northern United States are very rich in 

 members of this family. 



The aberrant family Bosminidae finds its only connection with 

 other Cladocera through this group by means of the remarkable 

 Macrothrix (?) pauper; and here it is only vaguely hinted at in the 

 elongated antennules and angled lower margin of shell, as well as 

 the presence of certain bodies near the base of the antennules. It 

 has been affirmed that none of the Lyncodaphnidae have an ephip- 

 pium, i. e. the saddle-shaped thickenino^ of the shell walls to in- 

 clude and protect the winter eggs; but I have discovered it in the 

 case of Macrothrix tenuicornis, Kurz, and presume it may occur 

 exceptionally in others. Kurz says that Ilyocryptus has no moult 

 proper, but this probably refers only to the European I. sordidus. 

 The American species differs from the generic description given by 

 Kurz, and may be different in this respect also. 



In this family the regularity in the disposition of the setae on 

 the antennae is broken and the fringing of these hairs serves the 

 purpose of specific distinction. The antennules are always long 

 and frequently differ considerably in the sexes. The pigment fleck 

 is always present (Kurz is in error in denying its existence in La- 

 thonura). In many forms there is no free posterior margin of the 

 valves, while the lower is generally thickly beset with movable 

 spines. The Lyncodaphnidae will be distinguished from Cerio- 

 daphnia, which they resemble, by their motion, which is a succession 

 of quick bounds, while the broader Ceriodaphniae hobble along as 

 though heavily weighted by the enormous mass of eggs with which 

 they are generally laden. The abdomen is usually short and the 

 anus is behind the terminal claws, but in Ilyocryptus the claws are 

 long and spined at the base. In the American I. spinifer the anal 

 opening is elevated to a point nearly underneath the stylets, and 

 there is a rudimentary anal caecum as in Lynceids. 



The males have the opening of the vasa deterentia in front of 

 the claws, which may be absent; the antennules are also modified, 

 being longer and curved. In Lathonura the abdomen is elongated 



1 Notes on some Minnesota Cladocera. 1881. 



