102 THE NAUTILUS. 



THE LAND MOLLUSKS OF THE BELGIAN CONGO.* 



BY T. D. A. COCKERELL. 



The American Museum of Natural History has issued a series 

 of reports on its Congo Expedition, all characterized by fullness 

 of treatment and abundant and beautiful illustrations. Other 

 similar reports are in course of preparation. The completed 

 series will constitute a guide to the zoology of equatorial Africa, 

 full of interest for the general naturalist and evolutionist, as 

 well as for specialists in the several departments. Among these 

 reports one of the most interesting is that on the Land Mol- 

 lusks, by Dr. Pilsbry. The presentation of the subject is so 

 clear and complete, and the illustrations are so good, that the 

 reader has no difficulty in understanding the characters of the 

 fauna, though he may have known very little about it before. 

 To one accustomed to the mollusks of America or Europe, the 

 tropical African series seems to belong to another world. Even 

 when there is a certain similarity of form, as among the Heli- 

 cida3, the anatomy shows that we are dealing with strange generic 

 types. The closest affinity is of course with the fauna of the 

 Oriental region, yet even that is remote, although some doubt- 

 less very ancient genera range through tropical Asia and Africa. 

 There is here a rather close parallel between the distribution of 

 the land mollusks and the fresh-water fishes. Certain genera 

 of fishes, but with distinct species, occur in the fresh waters of 

 India and of tropical Africa, but the latter region has many re- 

 markable types of its own, in some cases much more allied to 

 neotropical genera than to anything in India. It is evident 

 that Africa, the land of the okapi and the tsetse fly, is a store- 

 house of ancient groups of animals, some of which at least, were 

 formerly much more widely spread. While we thus emphasize 

 the probable antiquity of various African groups or genera, we 

 find remarkable specific diversity, apparently indicating that 



* Henry A. Pilsbry. A Review of the Land Mollusks of the Belgian Congo, 

 chiefly based on the collections of the American Museum Congo Expedition, 

 1909-1915. Bulletin American Mnseum of Natural History, Vol. XL, p. 

 370, 23 plates (8 colored), 1919. 



