xii PREFACE. 



lakes. This analysis points at once to the close affinity of the Jordan 

 with the rivers of Tropical Africa. The affinity is not only of species, 

 but of genera, for Chromis and Hemichroniis are peculiarly Ethiopian 

 forms, while the other species are identical with, or very closely allied to, 

 the fishes from other freshwaters of Syria. But the African forms are a 

 very large proportion of the whole, and considering the difficulty of 

 transportation in the case of freshwater fishes, the peculiarities of this 

 portion of the Fauna are of great significance. 



Turning to the Invertebrate Fauna, we find the Mollusca, terrestrial 

 and fluviatile, to amount to 213 species, of which 57 are common European 

 or Mediterranean forms, 8 Nilotic, and 8 other fluviatile species found also 

 in the rivers of the Indian Ocean, the Tigris, or Euphrates. About 

 140 species occur which have not as yet been noticed out of Palestine. 

 But many of these have no special significance in a geographical jDoint of 

 view. The land shells are for the most part merely modifications of wide- 

 spread Paleearctic forms, such as the 28 peculiar species of Claiisilia. It 

 must be remembered that in no department of zoology do we meet with 

 so many localized forms in limited areas as among the Pulmonifera, where 

 variations appear in many cases rapidly to follow segregation, while other 

 species extend with but slight modifications over an entire region. Thus 

 most of the species of Helix in the Southern Desert show affinities to the 

 Ethiopian type, while a peculiar group of Helices seems to have been 

 developed in the highland districts, between the desert and Lebanon ; of 

 which H. cariosa may be regarded as the typical species. But in the 

 Jordan valley are two groups of peculiar gasteropods. One group, found 

 only by the Dead Sea, is a series of modifications of desert forms, exempli- 

 fied in Helix prophetarum and H. filia. Another group, ot which Bulinms 

 labrosiis may be taken as typical, is found through the whole length of the 

 valley, and is a modification of a common Syrian and Asia Minor type. 



But the fluviatile molluscs are far more distinct. Besides such species 

 as Melania htbermlosa, extending from the west of Africa to China and 

 Southern India ; and Melanopsis buccinoidea, a common Mediterranean 

 form, we find various peculiar Unionidce and Melaniadce, such as Unio 

 simonis and U. episcopalis, which indicate very ancient separation from 

 any adjacent district, and the affinities of which are certainly not 

 Palaearctic. 



