NEW SPECIES OF SOUTH DAKOTA CRETACEOUS CRABS. 



By Mary J. Rathbun, 



Associate in Zoology, United States National Museum. 



The fossil crabs described below were sent to the United States 

 National Museum for identification by Mr. W. H. Over, of the Univer- 

 sity of South Dakota, Vermilion, South Dakota. They were col- 

 lected by Mr. Over in the Pierre Shales, partly at Indian Creek, 

 Pennington County, in the summer of 1914, but chiefly at Eastern, 

 Corson County, in the summer of 1915. 



The most numerous form represents a new type of Dromiacean for 

 which it is necessary to construct a new superfamily. The two 

 remaining species are referred to known genera. 



The type-specimens have been given to the United States National 

 Museum, while duplicates are in the collection of the University of 

 South Dakota. 



Tribe BRACHYURA. 

 Subtribe Dromiacea. 



In this subtribe the oviducts perforate the coxae of the second pair 

 of ambulatory legs, while the semmal ducts perforate the coxae of the 

 last pair of legs. The last pair of legs are dorsal in position and nearly 

 always prehensile, slender, and reduced in size. 



DAKOTICANCROIDEAE, new superfamily. 



Sternum of female without longitudinal grooves. Eyes sheltered 

 by orbits when retracted. No lineae anomuricae. 



This superfamily is made necessary, because the species here de- 

 scribed can not be placed in the Dromioideae, in which the sternum 

 of the female has longitudinal grooves, nor in the Homoloideae, in 

 which the eyes are incompletely or not at all sheltered by orbits, and 

 lineae anomuricae are nearly always present. 



DAKOTICANCRIDAE, new family. 



Same characters as those of the superfamily. 



DAKOTICANCER, new genus. 



Carapace transverse, thick, deeply grooved. Front, between the 

 eyes, small. Orbits well defined; eyes small, tapering. Outer max- 



Proceedings U. S. National Museum, Vol. 52-No. 2182. 

 65008°— Proc.N.M.vol.52— 17 25 385 



