ENTOMOSTRACA OF MINNESOTA. 179 



*Siinocephalus serrulatus Koch.. 



Daphnia serrtilaia — Koch, Lievin, Fischer, Lilljeborg. 



Head narrow, extending anteriorly into a sharp spiny angle in front 

 of the eye. Dorsal line of the shell abruptly angled or curved pos- 

 teriorly, projecting to form a broad obtuse spine behind; this spine is 

 serrate with sharp teeth and lies somewhat above the middle of the 

 height of the animal, so that the free posterior margins of the shell 

 fall much short of reaching the greatest height of the shell. Post- 

 abmomen of the usual form, with the claws armed with two series of 

 opines or bristles, the outer being much the larger; anal teeth curved 

 or angled, dentate; pigment fleck triangular or rhomboidal. Length 

 2.0 to 2.5 mm. 



I am not sure that the three following species are more than varie- 

 ties; the first in particular is very close to the European type. 



[* Sinioceplialus aniericanus Birge.] 

 Plate XLV, Fig. 9. 



My own observations of this form made throughout the Mississippi 

 Yalley are not in complete accord with the description of Birge, but 

 it seems improbable that there is any mistake in the identification. 

 The very generally distributed form on which this species rests is 

 subject to marked variations within certain limits. This species dif- 

 fers from S. serrnlatus in the following points. The head, although 

 prominent and spiny near the eye, is not angled between this promi- 

 nence and the beak; in fact, it is either straight or simply curved. 

 The pigment fleck is usually rhomboidal and only occasionally oval, 

 triangular or irregular. In other respects the agreement is rather 

 close; the terminal claws have two series of spines, one of which is 

 larger (not, as said by Birge, equal); the outer series is not so much 

 larger as in *S'. rostratus, but not nearly as inconspicuous as in 8. vetulus. 

 The terminal claws are rather evenly curved. This species is frequently 

 colored with pink or brown markings. In old females the back is 

 squarely angled above, forming a pocket for the eggs. The size falls 

 short of that of the last species. I have found this species from the 

 Gulf of Mexico to Minnesota. Professor Birge now recognizes this as 

 S. serrulatus. 



* Sinioceplialus rostratus Herrick. 

 Herrick '84. 



This form is of the size and color of 8. amertcanus, and approaches 



nearest to Schoedler's 8. exspiyiosus in general characters. The back is 



arched above but not abruptly angled; the spine is as in 8. amerkmms 



but not so low. The free posterior shell margins are somewhat shorter 



12 



