Decbmbkr 14, 1900.] 



SCIENCE. 



929 



One person was elected to active member- 

 ship. 



William Treleasb, 

 Recording Secretary. 



DISCUSSION AND CORRESPONDENCE. 



VON IHBRING'B AKCHIPLATA-ABCHBLEMI8 

 THEOEY. 



In Science for December 7th, Dr. H. von 

 Ihering gives a condensed statement of his 

 views on the origin of the South American 

 fauna. This is the more welcome, since the 

 original publications of v. Ihering, although 

 dating back to 1890, are not very well known, 

 chiefly because these articles (of which v. Iher- 

 ing gives a list) have been published in period- 

 icals, in which hardly anybody would look for 

 them. Part of them are of a mere popular 

 character, while another part are too much out 

 of the way, and they do not, by their titles, 

 give any indication that we might look in them 

 for a discussion of zoogeographical topics of 

 general interest. 



As regards the chief idea of v. Ihering, that 

 South America consists, genetically, of two 

 different parts, Archiplata and Archamazonas, 

 which have become united subsequently, I am 

 of the opinion that this theory is well worth 

 discussion. Indeed, I have accepted this theory 

 in my studies of the distribution of the fresh- 

 water Decapods, and have been able to collect 

 further material in support of it. And further, 

 in the report on the Tertiary Invertebrates of 

 Patagonia, collected by the Princeton Expedi- 

 tion, which is in course of preparation, I shall 

 again refer to this theory as a very acceptable 

 one for the explanation of certain features in 

 the distribution of marine animals. There- 

 fore, I was much surprised to see that v. Iher- 

 ing refers to my studies on the freshwater 

 crabs and crayfishes as at variance with his 

 theory, for only in this sense I can interpret his 

 reference to my ' biologic ' barrier. 



My theory of a ' biocoenotic barrier ' formed by 

 the Pctamonidse (tropical fresh-water crabs) for 

 the Potamobiidse and Parastacidae (crayfishes, re- 

 stricted to the extratropical parts of either 

 hemisphere) was formulated to explain only the 

 Bipolarity of the latter groups, without any 

 reference to the special conditions in South 



America, but chiefly in respect to those prevail- 

 ing in the old world.* I shall discuss this 

 question again, f and shall pay particular at- 

 tention to the South American conditions with 

 reference to v. Ihering's theory : I think that 

 the South American Parastacidx are members 

 of the old Archiplatan fauna, and ai'e connected 

 genetically with the New Zealandian and Aus- 

 tralian Parastacidse, and have reached these 

 parts apparently by way of a land connection 

 across the Antarctic regions, while the South 

 American Potamocarcininse (subfamily of Pota- 

 monidx) are characteristic of the old Archama- 

 zonian fauna, and point possibly to a former 

 connection of the latter with Africa (v. Iher- 

 ing's Archhelenis). In this connection I must 

 add that v. Ihering's argument, given in the 

 article referred to, as to the coexistence of 

 Potamocarcininse and Parastacidse in southern 

 Brazil is probably a mistake : there are to my 

 knowledge no Potamocarcininse in southern 

 Brazil, but the fresh-water crabs of small size, 

 to which he probably alludes, are Trichodaety- 

 linse, the genetic relations of which are doubt- 

 ful. They have nothing at all to do with my 

 ' biocoenotic barrier,' and certainly do not ' an- 

 nul ' it. 



In favor of the theory of a former disconnec- 

 tion of the northern and southern parts of South 

 America I may call attention to other consider- 

 ations. A communication of the Atlantic and 

 Pacific Oceans in Tertiary times is generally 

 accepted, and this connection is chiefly placed 

 at Panama. Now (according to Hill), J the 

 Isthmus of Panama was land since Mesozoic 

 times (with only an unimportant interruption 

 at the end of the Eocene); but Hill himself 

 admits that there must have been a connection 

 of oceans somewhere in the Tertiary. The 

 theory of v. Ihering gives us a clue to this. If 

 we move the interoceanic connection from 

 Panama southward, and construct it where 

 there must have been the sea separating Arch- 

 amazonas and Archiplata, that is to say, across 



* See ' Bipolaritaet ' in : Zool. Jahrb. Abt. f. 

 Sjst. V. 9. 1896, p. 593. 



f 'Decapoden' in Bronn's 'Klassen und Ordnungen, ' 

 vol. 5 Abteil. 2, p. 1289. This part has not yet been 

 issued, and I am quoting from proof sheets. 



iBuU. Mus. Comp. Zool., v. 28, No. 5, 1898. 



