42 ME. A.. MUKBAT ON THE GEOGEAPHICAL EELATIONS OE 



little room for change in appearance, there is a certain difference be- 

 tween the Indo-African species and the micro ty pal. Brazil has 

 only two or three of its own, and they have, to all appearance, 

 been derived from North America or the west of the Andes. And 

 there is again a difference between the European microtypal and 

 the North- American microtypal, the latter having a facies of their 

 own, which is shared by the Chilian and Peruvian species, and 

 also in a less degree by the Australian. 



In the Cassidas we have the well-marked North-American genus 

 Forphyraspis running down into Chili. In the Coccinellida), the 

 Ilippodamias (with the exception of one straggler in the Brazi- 

 lian region, and one or two on its borders near Quito and Bogota) 

 are entirely confined to the microtypal range, Chili being its 

 southern limit, but it has not been met with in Australia. Ooc- 

 cinella proper, however, which has a similar range to Ilippodamia, 

 occurs there, and one or two stragglers have also found their way 

 to the Cape, and one (C transversalis) to the Malayan region. 



The microtypal stirps in the southern extremity of South Ame- 

 rica is divided into two subfaunas by the Andes : that on their 

 western flank is merely a continuation of the fauna of Western 

 Peru ; that on the eastern flank is cut abruptly off on its northern 

 margin by the river Plata, where it meets the Brazilian type. 

 The demonstrated history of this country sufficiently explains 

 this distribution. Mr. Darwin in a few lines tells it thus : " The 

 landscape has one character from the Strait of Magellan along 

 the whole eastern coast of Patagonia to the Eio Colorado ; and it 

 appears that the same kind of country extends northerly in a 

 sweeping line as far as San Luis, and perhaps even further. To 

 the eastward of this line lies the basin of the comparatively damp 

 and green plains of Buenos Ayres. The former country, in- 

 cluding the sterile traversia of Mendoza and Patagonia, consists 

 of a bed of shingle worn smooth and accumulated by the waves of 

 a former sea ; while the formation of the Pampas (plains covered 

 by thistles, clover, and grass) is due to the estuary mud of the 

 Plata deposited under a different condition of circumstances." 

 (Darwin, Journal, p. 402.) In those days the water came quite 

 up to the mountains on the western as well as the eastern side ; 

 for we learn from the same source that " the valleys in the Cor- 

 dillera are filled with an immense thickness of stratified allu- 

 vium, which in all probability was accumulated at the bottoms of 

 deep arms of the sea, which, running from the inland basin, pene- 



