48 TWELPIH ANNUAL KEPORT. 



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 geaiculate. The pigment fleck is rhomboid 

 or pentagonal; the antennules are smoofh. The abdominal pro- 

 cesses 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, Missis- 

 sippi, aud was very carefully compared with S. americanus which 

 is also found there. 



Sp. 5. SimocephaUis exspinosus, Koch. 



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

 rhomboidal. Shell without a spine; maximum hight 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. cong-ener, Schoedler, 

 has the lower outline of the head sinuate instead of angled. 



Sp. 6. Simoceplialus daplinoides, Herrick. 

 American Naturalist. 1883. 



A curious transition form, found only south of the Tennessee 

 river, was described in the American Naturalist in May, 1883, under 

 this name. By an oversight a comparison made with S. americanus 

 appeared as though made with S. vetulus. The general shape is- 

 oval; the greatest hight of the valves lies near the middle and not 

 posterior to it as in all the other species. The head is short, de- 

 pressed, rounded in front; the beak is wanting; the lower margin 

 of the head is straight. The pigment fleck is small, oval or irreg- 

 ular: the fornices are small and short. The antennules are smooth. 



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

 terminal 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 extends into a blunt spine. In every detail, almost, 

 there is an approach toward the genius Daphnia, while the general 

 result is sufficiently like Simocephalus, The lower angle of the 

 shell is not armed with the peculiar curved spines as in all the other 



