466 LAND ANIMALS 



is an analogy, for example, between the snail fauna of Arabia and that 

 of Lower California: Helix (Micrarionta) areolata in California dif- 

 fers from its relatives from the moist regions of that locality and re- 

 sembles the Arabian subgenus Ereminia; furthermore, the Lower 

 Californian Bulimulus of the subgenus Sonorina parallels the Arabian 

 Buliminus of the subgenus Euryptyxis, and the Bulimulus (Orthos- 

 tomium) pallidior of Lower California in general form, and sculpturing 

 of the beginning whorls, is very similar to the Bulimunis {Cerastus) 

 fragosus of Yemen. 76 The species of the Lower Californian Bulimulus, 

 and others from similarly dry and desert areas in Peru and Chile, carry 

 the stamp of their environment so plainly that in many cases similar 

 forms from California and Peru were placed in the same species, and 

 only careful investigation established that their resemblances were 

 due to independent convergence. 77 



In the North African and Asiatic deserts occur white isopods with 

 high curved backs, whose form produces a relative reduction of the 

 surface, particularly in the genus Hemilepistus, but also in species of 

 Porcellio and Metoponorthus; apparently in these too, as in our north- 

 ern species of Porcellio and Armadillidium , evaporation is reduced by a 

 reduction of the epidermal glands. 



As elsewhere in open lands, running, jumping, and burrowing ver- 

 tebrates play an important role in the desert. Lizards are runners, as 

 are the larks and coursers (Cursorius) among the birds. Jumping mice 

 are the best representatives of the jumping animals. Burrowing ani- 

 mals are at home in the sand deserts. Reptiles are especially abundant ; 

 they are able to dig themselves into the sand very quickly. The species 

 of Phrynocephalus and Phrynosoma produce horizontal movements 

 with their flat bodies and disappear immediately into the sand, which 

 covers them. In many snakes and lizards of the desert, the rostrum 

 is particularly well developed and extends over the mouth; they bur- 

 row through the sand by means of lateral movements of the head. 

 Beetles, too, burrow into the loose soil. In the Sahara, the crested larks, 

 Galerida cristata, are said to have longer beaks in sandy than in rocky 

 desert, which enables them to extract such prey out of the sand. 



Wherever the desert floor is sandy, many animals have adaptations 

 which prevent them from sinking into the sand and so facilitate run- 

 ning over the loose ground. Among the lizards, the toes are provided 

 with lateral rows of scales or fringes, a convergent development in 

 response to the living conditions which is shown by the iguanid U?na 

 of the Colorado desert, the geckonids Ptenopus in South Africa (Fig. 

 115) and Teratoscincus of the Asiatic deserts, the agamid Phryno- 



