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Of considerable significance is the thysanuran genus Machilinus. 

 While Machilinus has not yet been found in South Africa or India its 

 distribution is otherwise remarkably like that of Mecidea. Wygodzin- 

 sky (1950) calls attention to the minimal possibilities for the active or 

 passive dispersal of machilids and concludes that distribution in this 

 instance is an argument indicating the considerable age of the genus 

 Machilinus. 



At least two genera are known that provide examples of this 

 distribution pattern, both at the generic and at the specific levels. 

 The first of these is the genus Leptoconops, which belongs to the 

 dipterous family Heleidae. This family includes the biting midges and 

 punkies, which are commonly associated with aquatic environments; 

 nevertheless, Leptoconops is largely restricted to arid or semiarid 

 regions lying between the parallels of latitude 40° N. and 35° S. 

 Three species are known from Australia, two from South Africa, five 

 from the Mediterranean basin, two from the lower Oriental region, one 

 from South America, and two from North America. In the revision 

 of the genus by Carter (1921), one of the North American species, 

 which has been extremely abundant near Great Salt Lake since that 

 region was first visited by white man, was described as var. americanus 

 of the North Africa species kerteszi Kieff er. Subsequent workers have 

 reviewed and accepted Carter's opinion. 



Finally, there is the leafhopper genus Circulifer, which is of interest 

 since it contains the beet leafhopper C. tenellus (Baker). The beet 

 leafhopper occurs in the western United States, in xerophytic environ- 

 ments in southern Florida, and in Puerto Rico and the Mediterranean 

 basin. With the exception of tenellus, Ciculijer appears to be re- 

 stricted to the arid and semiarid parts of the Mediterranean basin 

 eastward to Central Asia. The fact that tenellus belongs to Circulifer 

 was shown by Oman (1948), and though he emphasized its Old World 

 distribution and relationships, he did not undertake to explain the 

 species' distribution. Of all the cases discussed here, it seems likely 

 that the strongest argument in favor of a recent introduction can be 

 presented for this leafhopper. Nevertheless, together with Lepto- 

 conops kerteszi, Circulifer tenellus has a distribution pattern closely 

 parallel to that for the combined species Medicea pallida, longula, and 

 major. 



It therefore appears that in all categories from the family to the 

 species, examples can be cited that point to an ancient faunistic and 

 floristic relationship between the semidesert and desert regions of the 

 Mediterranean basin. South Africa, southern South America, and 

 southwestern North America. Far from being peculiar, the distri- 

 bution of Mecidea in fact fits a rather well-established pattern. 

 Clearly, the genus should be considered in futiu-e speculations con- 



