BURTOA. 299 



streaks along growth-lines, chiefly on the last whorl. Plicat- 

 ulate, cut by spiral lines, generally smoother below the periph- 

 ery. Whorls 6y 2 -S (the early ones smooth when unworn?). 

 Peristome more or less roseate, unexpanded except the colu- 

 mellar lip, which is rolled back or reflexed. Columella some- 

 what concave above, and obliquely subtruncate at the base 

 in immature individuals, often not noticeably so in adults. 

 Type, Burtoa nilotica. 



Distribution, tropical East Africa, from the headwaters of 

 the Nile to Matebele Land, especially in the Lake region. 



Burtoa was established before.Lmw/iacm for the forms of 

 the Limicolaria nilotica group known to Bourguignat, and 

 with a diagnosis applying exclusively to these forms, one of 

 which is expressly designated as the type of the genus (see 

 last paragraph on p. 90 of Bourguignat 's Mollusques de 

 I'Afrique Equatoriale) . Bulimus kraussi Pfr. was also com- 

 prised in the list of species, but it is excluded by the terms 

 of the description. The name Livinhacia of Crosse has been 

 used for Burtoa by most authors, but it is of later date and 

 proposed for the same species, L. nilotica having been named 

 as its type. 



The species of Burtoa resemble the large South American 

 Bulimi of the Borus group in stature and coloring. They 

 seem to abound around Lake Victoria Nyanza, in a vast vari- 

 ety of local forms and races. The rank of these is at present 

 wholly uncertain, and no existing data show whether all the 

 forms of the Lake region are referable to nilotica as sub- 

 species, or whether a number of species occur in this area. 

 Probably one view is as good as another. 



The soft anatomy of this group is unknown. It differs 

 from Achatina by the perforate axis and obsolescence of the 

 columellar truncation in adult shells. The young are more 

 or less distinctly truncate basally. No form of Burtoa shows 

 any trace of zigzag or oblique color-stripes, so prevalent in 

 Achatina, Limicolaria, etc. In place of them, there are deep 

 chestnut- colored streaks along the growth-lines. It is not 

 without significance that no species or specimens of Burtoa 

 have been found with the characteristic decoration of Acha- 



