1902.] AND ANCIENT GEOGRAPHY. oS9 



occurred at this time. The African stock of the Potamonino'. 

 remains practically unchanged, the Ma'/ai>asstan forms alone 

 becoming separated from it ; the Indian stock spreads over the 

 Malaysian islands to North Australia and Japan,^ and further, 

 sends out a westward bran(-h over western Asia, reaching Southern 

 Europe and Northern Africa. 



D. Distribution of ^glea and the TRicHODACTVLiNiE. 

 (Compare Fig. 2, p. 296, and Fig. 4, p. 311.) 



1. The remarkable resemblance of the range oi ^glea to that of 

 Parastacus suggests identity of origin. This would mean that 

 yEglea, in the beginning of the Tertiary, inhabited Chdi, and 

 migrated, at this time, into northern Argentina 2.\iA southern Br aziL 

 Since there are no closer relations to this peculiar genus in any 

 other part of the world, ^glea apparently is indigenous to ("hili, 

 i.e., to the northern extremity of the American part of Archinotis^ 

 and subsequently extended only into the southern part o{ A>chiplata. 

 Of course, the opposite direction of migration also is possible. 



2. As we have seen above (p. 312) the distribution of the Iricho- 

 dactylince offers no remarkable feature. It belongs to the Atlantic 

 slope ot i>resent South America (the Neotropical region of Wallace) 

 and seems to have formed under the recent conditions. Possibly, 

 this subfamily is a new addition to the freshwater fauna, and immi- 

 grated from the marii.e litto-ral of the Atlantic. Further investiga- 

 tion of this question, together with a closer study of the morpho- 

 logy and systematic relations of this group are very desirable.^ 



PART III, CLIMATIC AND BIOCOENOTIC^ BARRIERS TO THE 

 DISTRIBUTION OF CRAYFISHES AND CRABS. 



In the foregoing discussions we have repeatedly called attention 

 to some distributional facts which we were unable to explain. For 



^ This extension began po^-sibly as early as the Upper Cretaceous and Lower 

 Tertiary. 



2 Everything here depends on the systematic position and affinity of this group. 

 If it should be a primitive one, and leally btlong to the Potamonidce, it is 

 possible that it reached Brazil in i-ower Cretaceous times, when it formed part of 

 Archhelenis. Its isolation in Upper Cretaceous Archiplata, which was not fally 

 destroyed when it became a part of Lozver Tertiary Neonotis, would explain its 

 isolated morphological position. In the Tertiary ihis subfamily would then have 

 extended its range northward. 



3 As to the term " Biocoen')tic barrier," compare Ortmann, Grundzuege der 

 marinen Thiergeographie, iSpb, pp. 41 and 70. 



