108 ZOOTECUS. 



panded. The columellar margin is dilated, thickened, and 

 arches over the very small umbilicus. 



The species is excessively variable, but the typical form is 

 small, specimens measuring as follows: 



Length 10, diam. above aperture 3.8 mm., whorls 8%. 



Length 9, diam. above aperture 3.3 mm., whorls iy 2 . 



Length 8, diam. above aperture 3.2 mm., whorls 7 1 /4- 



This small form is common in Arabia and India. The shell 

 is thinner and usually more whitish-corneous, less opaque- 

 white than the larger forms. 



Shells of the same general type but more robust have been 

 found in both Africa and India, and numerous nominal 

 species have been based upon them. It is quite likely that 

 some of these may be found to be local races worthy of re- 

 cognition by name ; but pending a thorough study of the sub- 

 ject by some naturalist with the requisite local knowledge, 

 it seems best to give in this place merely the original docu- 

 ments, with such notes on the shells and figures as may 

 seem useful. 



African forms. 



In Eastern Africa Z. insularis has been reported from 

 Egypt (Letourneaux) ; around Massaua, in the Bogos country 

 and on the Hamacen plateau, Abyssinia (Raff ray) ; western 

 shore of Lake Stephanie, British East Africa (Dr. A. Donald- 

 son Smith, 1896). Much further west it has been found at 

 Oued-Anissait, north of Insala, in the Algerian Sahara, a 

 place in about 27 N. Lat., nearly south from Algiers (Soleil- 

 let, B. soleilleti Bgt.). Still further west it occurs in Sene- 

 gambia (coll. A. N. S. P.) and on the Cape Verde Islands, 

 where it is known as B. subdiaphanus King. 



The specimens collected by Dr. A. D. Smith at Lake Steph- 

 anie are quite cylindric, sharply finely striate, with the 

 characteristic decussating spiral grooves (pi. 26, fig. 22). 

 They measure from 10 x 4.2 to 11 x 4 mm., whorls 7% to 8. 

 The parietal callus is not very thick. 



Bourguignat's specimens from the Algerian Sahara de- 

 scribed as B. soleilleti (Species noviss. Moll, in Eur. Syst. 



