]80 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



than the greatest height of the shell. The head is produced below the 

 eyes in an angle like a right angle, which is not spiny. The lower 

 margin of the head is excavated to form a right angle, and in front of 

 the smooth antennules forms a very prominent beak, beyond which 

 the antennules reach but a S'hort distance. The terminal claws of the 

 post-abdomen are straightish and are more heavily spined than 

 in the preceding; the anal spines are doubly curved or geniculate. 

 The pigment fleck is rhomboid or pentagonal; the antennules are 

 smooth. The abdominal processes differ somewhat from the previous 

 species, in which the second one is rounded above, for in this it is 

 squarely truncate. This species was found only in shallow pools at 

 Ocean Springs, Miss., and was very carefully compared with ^S*. ameri- 

 canus, which is also found there. 



Simocephalus exspinosiis Koch. 



Head extending into an obtuse angle at the eye, pigment fleck 

 rhomboidal. Shell without a spine; maximum height of the shell 

 greater than that of the free posterior margin. Caudal claws with an 

 unequal series of spines; anal spines evenly curved. There is little 

 to distinguish the above from this species save the geniculate anal 

 spines and the presence of a blunt spine on the shell. 



Var. congener Schoedler has the lower outline of the head sinuate 

 instead of angled. 



* Simocephalus daphnoides Herrick. 



Plate XLVI, Figs. 5,6. 



Herrick '83. 



A curious transition form, found only south of the Tennessee river^ 

 was described in the American Naturalist for May, 1883, under this 

 name. By an oversight a comparison made with ti. americanus ap- 

 peared as though made with S. vetulus. The general shape is ovalj 

 the greatest height of the valves lies near the middle and not posterior 

 to it as in all the other species. The head is short, depressed, rounded 

 in front; the beak is wanting; the lower margin of the head is straight. 

 The pigment fleck is small, oval or irregular; the fornices are small 

 and short. The antennules are smooth. 



The post-abdomen is narrow, shaped more as in Daphnia; the ter- 

 minal claws are straightish and fringed part way with spines; the anal 

 spines are slightly curved. The i^rocesses of the abdomen are long, as 

 in Daphnia. The shell is covered by the characteristic striations and 

 extend into a blunt spine. In every detail, almost, there is an ap- 

 proach toward the genus Daphnia, while the general result is sufi&- 



