180 © 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 short 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 exspinosus 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, Fias. 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 S. americanus ap- 
peared as though made with S. vetulus. The general shape is oval; 
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 Dane the ter- 
minal claws are straightish and fringed part way with spines; the anal 
Spines are slightly curved. The processes 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 suffi- 
