366 



Mareotis, figured by Reeve as Physa vitraea, which we regard as 

 identical with Bulinus senegalensis O. F. Miiller. 



Length 



Width 



Aj 



?. Length 



A p. 



Width 





10.5 



4.0 





4.5 



2.0 



mm. 



Cotype 

 lemiplicata, Fig. 15 



11.5 



4.5 





4.0 



2.0 





a 



11.0 



4.5 





5.0 



2.0 





" 



11.0 



4.5 





4.5 



2.0 





a 



8.0 



3.5 





2.5 



1.8 





Egypt, Fig. 16 



7.2 



2.5 





2.4 



1.5 





a 



7.5 



2.2 





2.3 



1.5 





it 



Bulinus (Pyrgophysa) wahlbergi (Krauss). 

 Plate 18, figure 17. 



Pyrgophysa scalaris Dautzenberg 1890, Mem. Soc. Zool. 

 France 3, p. 133, pi. 1, figs. 12a-b. Not Physa scalaris Dunker. 



A numerous series collected by the senior author at Albert- 

 ville, Belgian Congo, in a swamp on the shores of Lake Tangan- 

 yika, are readily distinguished from B. forskalii by the more 

 slender outline and the deeply contracted sutures. Among the 

 published figures they agree best with Physa wahlbergi Krauss, 

 described from the Limpopo River, Transvaal, as well as with 

 Dautzenberg's supposed scalaris from Bakel, Senegambia. As 

 we have shown above, the true Physa scalaris Dunker appears to 

 be identical with B. forskalii. 



The following measurements are based upon the Albertville 

 series. 



Fig. 17 



B. wahlbergi, as here understood, is in our opinion a distinct 

 species. What Sowerby (1873, Conch. Icon. 19, Physa, pi. 8, 

 fig. 58) has figured as 'Physa walbergii,'' from the Nile, is an 

 entirely different form, which appears to be identical with B. 

 forskalii. 



There has been only one previous record of a Pyrgophysa from 

 Lake Tanganyika, viz., that of Germain (1908, Res. Scientif. 

 Voy. Afrique Fod, p. 640), who recorded Physa dunkeri Germain 



Length 



Width 



Ap. Length 



Ap. Width 



8.0 



3.0 



3.0 



1.5 mm. 



8.5 



3.0 



4.0 



1.5 



ro.4 



3.5 



3.0 



2.0 



8.5 



3.0 



2.8 



1.5 



