Vil ames DISTRIBUTION OF CRAYFISHES Zia 
that they are part of a relict marine fauna. It would appear 
that they have been differentiated in the lake itself during 
a long period of isolation. 
Two groups of Brachyura, viz. the Thelphusidae and the 
Sesarminae (a sub-family of the Grapsidae), are fresh - water. 
Thelphusa fluviatilis is an inhabitant of North Africa, and 
penetrates into the temperate regions of the Mediterranean, and 
is said to be exceedingly common in the Alban Lake near Rome. 
Both these families have representatives on land, e.g. Potamo- 
carcinus in Central and South America, and certain species of 
Sesarma, and the closely related Gecarcinidae of the West Indies. 
The remaining families to be dealt with are the two Cray- 
fish familes — the Astacidae and the Parastacidae — which 
live in rapidly moving rivers and streams, and occasionally in 
lakes. A few species of both families have taken to a 
subterranean mode of life, and excavate burrows in the earth, 
e.g. the Tasmanian Crayfish, Hngaeus fossor. The distribution of 
the Crayfishes has long engaged the attention of naturalists. 
It was first seriously studied by Huxley,' and has subsequently 
been followed up, especially in North America, by Faxon” 
and Ortmann,® but our knowledge of the South American and 
Australian forms is still very incomplete. The Astacidae in- 
habit the northern temperate hemisphere, the Parastacidae the 
southern temperate hemisphere, the tropical belt being practi- 
cally destitute of Crayfishes. Of the Astacidae the genus 
Astacus (Potamobius), including the common Crayfishes of 
Europe, occurs in Europe and in North America west of the 
Rockies. The genus Cambaroides, which in certain respects 
approaches Cambarus, is found in Japan and Eastern Asia. The 
very large genus Cambarus, on the other hand, only occurs in 
North America east of the Rockies, so that Cambaroides occupies 
a very isolated position. The occurrence of a Cambarus, C. 
stygius, in the caves of Carniola, has been recorded by Joseph, so 
that it would appear that this genus had a much wider range 
formerly than now. 
Of the southern temperate Parastacidae, Australia and 
Tasmania have the genera Astacopsis and Hngaeus; New Zealand 
1 The Crayfish, Internat. Scient. Series. 
2 Mem. Harvard. Mus. x., 1885. 
3 Proc. Amer. Phil. Soc. xli., 1902, p. 267, and xliv., 1905, p. 91. 
