36 MR. A. MUKEAT ON THE GEOGRAPHICAL RELATIONS OF 



The above are not the only points in which Professor Heer's 

 Miocene species lend important help to the student of geogra- 

 phical distribution. They are of essential assistance in deter- 

 mining the southern limit of the microtypal stirps in Europe 

 and Asia, and whether some of the forms which are found in the 

 southern part of the European range really belong to it, or are 

 immigrants from the African or Indian region lying to its south. 

 The South-European fauna is composed partly of the same species 

 as that of the districts more to the north, partly of distinct species 

 of the same genera, and partly of what may be regarded as 

 modified forms of the same general stock, but having a consider- 

 able effect in altering the facies of the fauna. Besides these, 

 there are a few (perhaps in all not more than ten or twelve) 

 species which have probably sprung from the African stirps, and 

 established themselves in Europe by immigration. The southern 

 limits of the fauna of this region, which extends along the bed of 

 the Sahara onwards to the Caspian and Mongolian Steppes, are 

 the deserts of the Sahara, which cut it off from Europe, and the 

 Himalayan range, which divides it from India and China. As 

 regards the Sahara, it is its southern border which is the limit. 

 Its bed seems to have been raised by a force operating from the 

 north. The strata, abutting on the Atlas mountain-range, rest 

 inclined on its flanks as if tilted up by it. The effect of this 

 elevating force operating in the north would, of course, be to 

 raise the part of the Sahara nearest it first out of the water ; the 

 last vestige of the sea would be at the south, consequently the 

 bed to the north would be first colonized, and it could only be so 

 from the north. The facts of geographical distribution quite cor- 

 respond with this view. The fauna and flora of the desert is 

 Mediterranean, not Senegalese. 



Returning to the Asiatic terminus of the microtypal stirps, 

 let us now endeavour to trace its further course. The genus 

 Blaps, which is a characteristic feature in the Coleopterous fauna of 

 Central Asia, will furnish us with the means. It may be taken as 

 a representative case applicable to other species also, although it 

 certainly is the most striking instance which occurs to me. Up- 

 wards of 100 different species of Blaps, out of a total of about 150, 

 have been described as inhabiting the country between Southern 

 Russia, Mongolia, and Mantchouria. Now if we cross to Cali- 

 fornia in continuation of the same line we have not Blaps, but 

 we have Blaps's brother, and he has been a twin. We have 



