312 ORTMA.NN — DISTRIBUTION. OF DECAPODS [April 3, 



Nicaragua. It is to be remarked that none of the localities is 

 situated in the drainage of the Pacific Ocean, but all are in that of 

 the Atlantic. 1 



This distribution does not offer any remarkable facts. The 

 Trie ho dacty lince seem to belong to the tropical parts of the 

 Atlantic slope of South America, and their centre is somewhere in 

 Brazil; from Brazil they extend in every direction until, in the 

 east the Atlantic Ocean, in the west the Cordilleras, in the 

 south the climate of Argentina form barriers. To the north the 

 most advanced station is in Nicaragua ; here no natural boundary 

 (climatic or topographic) is marked. 



Further speculations as to the distribution of this subfamily do 

 not seem to be very promising until we are better acquainted with 

 the chorological facts. The whole appearance presented by the 

 distribution is a recent one ; probably it is continuous and, in 

 most directions, limited by natural boundaries. In this respect it 

 is strikingly distinguished from the other groups of the family 

 Potamonidce discussed above. 



I have the impression that the Tri c ho da cty lince are not so closely 

 connected, systematically, with the other subfamilies of the Pota- 

 monidce as was believed hitherto. In fact, transitional forms to any 

 of the other subfamilies are not known, and the Tri cho dacty lince 

 are morphologically isolated and sharply defined. Moreover, the 

 whole "habitus" of these crabs is so entirely different from that 

 of the Pctamocarcininoz that it is worth while to revise the syste- 

 matic relations of these groups. As I venture to imagine, it will 

 be found, possibly, that the Trichodacty lince form a group that is 

 much more sharply isolated, systematically, and that has little to 

 do with the family Potamonidce. This much is evident : according 

 to its morphologic isolation, we ought to expect that the Tricho- 

 dactylince are a comparatively ancient group ; but this is contra- 

 dicted by their distribution, which possesses a remarkably recent 

 character. 



These are the reasons why we shall exclude the Trichodacty lince 

 from our further discussions. 



1 This is contrary to what we have in the Pota?nocarcinince, which are found 

 also on the Pacific slope in Ecuador, and especially in Central America and 

 Mexico. 



