Freshwater Crustacea of the Indian Archipelago. 253 



species of Gelasimus, and Sesarma bidens. These genuine 

 marine animals I obtained, it is true, not in fresh, but still in 

 brackish water. They have consequently arrived to some 

 extent at the first stage of immigration. 



Our list thus teaches us that of seventy-six species of Deca- 

 pods found in fresh water, and therein mentioned, twenty- 

 nine certainly live both in brackish and salt water, and the 

 latter total undoubtedly falls a long way short of the truth. 

 Further, while among Decapods fresh water in Europe con- 

 tains only Astacus jluviatilis, Telphusa fluviatilis, Latr., 

 Pilumnus tridentatus, Maitland, Ilemicaridina Desmarestii, 

 Millet, Leander Edicardsi, Heller, Pahemonetes varians. 

 Leach, and Troglocaris Schmidtii, in the Indian Archipelago 

 it yields in all probability considerably more than eighty 

 species. 



Consequently with regard to the Decapods also the fresh- 

 water fauna of India is as different from that of Europe as it 

 can possibly be • and as to these Decapods, it may be asserted 

 that the majority are distinctly immigrants from the sea. On 

 summing up the results of our discussion the following con- 

 clusion may well be pronounced : — 



The Crustacean fauna of the fresh water in the Indian 

 Archipelago is composed of two different kinds of elements : 



1. Forms of universal occurrence, belonging to the Ento- 

 mostraca. In comparison with the fauna of Europe this 

 autochthonous freshwater constituent, which has numerous 

 means of dissemination, is but scantily developed. Apus and 

 DrancJupus are absent. 



2. Regional or local animals, which are destitute of the 

 aids to dissemination afforded by smallness of body and 

 special arrangement of the branchiae. It is true that, in so 

 far as they are parasites, they are capable of being trans- 

 ported. 



These regional Isopods, Amphipods, and Decapods derive 

 their origin directly or indirectly from the sea, and that by 

 means of immigration, which is also still in progress at the 

 present time, so that even now fresh elements are still con- 

 tinually being added to the freshwater fauna. 



This portion of the fauna is entirely different from that of 

 Europe, and the Indian freshwater fauna thus receives an 

 impress of quite another kind *. 



* [The remainder of the part is devoted to the description of new 

 species. — Transl.] 



Ann. & Mag. N. Hist. Ser. 6. Vol. xiv. 18 



