252 Dr. Max Weber on the 



1 . In the first place, out of the twenty genera that I met 

 with in fresh water, only Telphusa, with Geotelphusa and 

 Paratelphusa, and Atya occur in fresh water exclusively. 



2. The genera Caridina and Palcemon show only a pre- 

 ponderance of freshwater forms ; they contain species that 

 also occur in sea- or brackish water. Among ten species of 

 Caridina I found Caridina Wyckii and C. gracilirostris also 

 in brackish water. Out of twenty species of Palcemon from 

 fresh water I took P. carcinus also in the sea and in brackish 

 water. In the latter I further obtained Palcemon sundaicus, 

 P. lar, P. endehensis, and P. latimanus. 



3. We next come to genera that exist equally as well in 

 the sea as in rivers, with an intermediate habitat in brackish 

 water. This has already been recorded by Semper for Varuna 

 literata] I also found this animal in these three kinds of 

 water. Besides this species, however, and under similar con- 

 ditions — Ocypode cordimana, Utica gracilipes, and ten species 

 of Sesarma. Among the latter is one, Sesarma maculata, 

 which had already adapted itself to life upon land in moist 

 surroundings ; while among four species of Geosesarma I met 

 with one species upon land alone, and two others there and 

 also in fresh water. Lastly, Metasesarma also belongs to the 

 same division ; although I met with it, as also certain species 

 of Sesarma, only in fresh water, they will undoubtedly on 

 further search all be found also in the brackish or saline 

 portion of the river-mouths. Sesarma bidens I obtained only 

 in sea- and brackish water. 



4. Finally we have genera, such as are usually reckoned 

 as being exclusively marine, but which I likewise found in 

 fresh water. Here are to be mentioned two species of Pseudo- 

 grapsus, Pyxidognathus granulosus, five species of Ptycho- 

 gnathus, Leander concinnus, Penceus mofioceros, and, as very 

 noteworthy, Alpheus rapax, Pemipes testudinarius, and R. den- 

 ticulatifrons. The two latter were met with by my friend 

 A. Wichinann in the River Koinino, in Timor, in fresh 

 water. 



The four groups thus indicated, regarded in reversed order, 

 emphasize with sufficient clearness the immigration, still in 

 progress or already complete, of marine Decapods into the 

 rivers. This is obvious at once with respect to groups 3 and 

 4 but it also applies to Caridina and Palcemon. With 

 reference to Palcemon, I have already pointed out that immi- 

 gration from the sea is demonstrated to a certain extent by 

 means of the numerous species of Bopyridas which are para- 

 sitic upon these Indian freshwater prawns. 



In the list are also included Cardisoma carnifex, three 



