DESCRIPTIONS OF FOSSIL CRABS FROM CALIFORNIA. 



By Mary J. Rathbun, 



Assistant Curator, Division of Marine Invertebrates, U. 8. National Museum. 



This paper is based on specimens collected in California in 1907 

 by Dr. Ralph Arnold, Paleontologist, U. S. Geological Survey." 

 Three species are from the Miocene of Fresno and Kern connties; 

 the remaining species is from the Cretaceous beds of San Mateo 

 County. 



The Tertiary forms differ markedly from one another as to their 

 resemblance to existing- types. One is a species of Loxorhynchus 

 identical with L. grandis, which now occurs locally off the California 

 coast ; another is a Cancer which is distinct from any of the nine 

 recent species of the genus inhabiting California, but may be 

 the ancestor of one or more of them; while the third, probably a 

 Parthenopid, is quite unlike any now known. The degrees of rela- 

 tionship which these fossil crabs bear to their living allies corre- 

 spond to the age of the strata in which they are found, the Loxorhyn- 

 chus being stratigraphically above the Cancer, though both are in the 

 Miocene, and the Cancer in turn far above the Parthenopid, which is 

 also in the Miocene. 



The single species from the Cretaceous is a new type which I 

 have designated as Archceopus antennatus. In its dorsal aspect it 

 is allied to Plagiolophus vancouverensis Woodward from the Cre- 

 taceous of Vancouver Island. Of the latter species only the carapace 

 and fragments of the limbs are known, so that it is impossible to tell 

 whether it possesses the peculiar characters existing in Archceopus, 

 especially the rudimentary and elevated fifth pair of feet. More 

 interesting is the resemblance to the genus Retropluma (see below), 

 represented by an anomalous form from the depths of the Indian 

 Ocean, which was described by its authors as of an archaic type. 



a Doctor Arnold has furnished the notes on localities and also the lists of 

 fossils inserted here. 



Proceedings U. S. National Museum, Vol. XXXV— No. 1647. 



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