1902.] 



AND ANCIENT GEOGRAPHY. 



397 



The following are taken from Rathbun, U. S. Nat. Mus., Vol. 

 16, 1893: 



Pacific Side. 



Libinia macdonaldi 

 Rthb. 



Pelia (2 species). 

 Epialtus bitubercula- 



TUS. 



Atlantic Side. 



L. spinimana Rthb. 



Pelia (2 species). 



E. BITUBERCULATUS. 



Remarks. 



Other species known from 

 both sides, and possibly 

 from other parts of the 

 world, but these two are 

 especially closely allied. 



Genus found nowhere else. 



There are four other species 

 on the Pacific side. The 

 genus fcs found nowhere 

 else. 



The following is taken from Rathbun, ibid., Vol. t8, 1896, and 

 Proc. Biol. Soc. Wash., Vol. 10, 1897 : 



Callinectes (4 species). 



Callinectes (6 species). 



All Pacific species different 

 from the Atlantic. Three 

 of the Atlantic species 

 also found in West Africa. 

 Genus not found else- 

 where. 



The following is taken from Nobili, Boll. Mus. Torino, Vol. 16, 

 1901, p. 32: 



Cronius ruber (Lmck.) 



C. ruber. 



This species also in West 

 Africa, but nowhere else. 



In this list we see there are seven identical species. The rest are 

 more or less closely allied, but the affinity is always so close that it 

 is not equaled in any other part of the world, with the exception 

 of West Africa, where some of the types have been found that are 

 common to the east and west sides of America, but are lacking 

 everywhere else. This affinity of the West African littoral fauna is 

 a well-known fact, and there is nothing remarkable about it, since 

 a communication between both sides of the Atlantic is possible in 

 many cases even at present times. 



