412 PROCEEDINGS OF THE ACADEMY OF [1894. 



where it extends northward to southern France and southern Austria. 

 This nearly exclusive distribution within the tropics, at least in the 

 warmer climates, shows that the family was probably also in former 

 times an inhabitant of the warmer parts of the world, and the possi- 

 bility is granted that the immigration into fresh-water took place at 

 a time when climatic zones were not at all differentiated, a tropical 

 climate prevailing everywhere. If this immigration took place in 

 a later time, the poles having undergone a cooling, one could not 

 understand the presence of the family in all parts of the tropics, as 

 well as the occurrence of some genera (Xiphocaris, Caridina, Atya) 

 on both of the present great continents, the eastern and western. 



After the cooling of the northern and southern circumpolar regions 23 

 the range of the family was divided into two parts : an eastern com- 

 prising the tropical Africa, Asia, Australia, and the Pacific islands, 

 and a western comprising tropical America. 2 * The most primitive 

 genera of the family were restricted in range by the concurrence o* 

 the more extremely developed ones, and the latter preserved a more 

 circumtropical distribution. 



It is very interesting to examine the geographical range of the 

 genera and species from the point of view here given. 



The most primitive genus, Xiphocaris, shows a distribution the 

 peculiarity of which can only be understood by supposing that the 

 range of this genus was formerly a more extended one, but that in 

 most parts of the world the representatives were exterminated. Only 

 three species survived, one of which lives now in the fresh-waters oi 

 the West Indies, the other in Indo-Malaysia, from Japan to Australia, 

 and the third in New Zealand. From the intermediate countries 

 species of this genus are not recorded. The Indo-Malaysian species, 

 Xiphocaris compressa, repeats, as we know at present, this peculiarity 

 in a reduced manner, being only recorded from Japan, the island of 



23 See Ortmann Jenaische Denkschr., VIII, 1894, p. 74, and Pfeifer, Versuch 

 über die erdgeschichtliche Entwickelung der jetzigen Verbreitungsverhältnisse 

 unseres Thierwelt. Hamburg, 1891. 



24 In case the Atyidce immigrated from the sea into the fresh-water after 

 this separation, it is very probable that the geographical distribution would not 

 be a circumtropical one, but that different groups immigrated into the western 

 and eastern continents. We know another group of Decapoda, in which the 

 latter is the case: the family Telplmsidce, one subfamily of which the Telphus- 

 incz, being restricted to the tropical and subtropical parts of the eastern continents 

 (Mediterranean, African, Indian. Indo-Malaysian, etc.), two other subfamilies, 

 TrichodactylincB and Pseudotelphusince, being restricted to the tropical parts 

 of America. 



