Reference List of South African Non-marine Mollusca. 243 
Genus ISIDORA, Ehrenberg, 1831. 
(Symb. Phys., Evertebrata.) 
Type of Genus, I. hemprichii, Ehrn. (contorta, Mich.). 
Kobelt (1909) is probably correct in placing in this Genus all 
South African species formerly ascribed to Physa. Jivery one, 
whose animal has been examined, has proved to belong to Isidora, 
and it seems unlikely that Physa exists in the subcontinent. 
The Genus has suffered severely for a long time from misidenti- 
fication. It is the merest truism to remark that the speed of a 
stream and the nature of its soil have so great an effect on the shell 
of its molluscan inhabitants that colour, epidermal sculpture, and 
even substance or contour are of little account in the determination 
of fresh-water species ; yet many have been identified, and others 
founded, on these features alone, without reference to the form of 
the parietal and columellar regions, which appear to offer the only 
moderately stable basis for comparison. I regret that the results of 
my investigation so far have been of a purely destructive nature, but 
fear that even more of this will be necessary before it is advisable to 
describe the one or two new species which possibly exist in South 
Africa. Mr. E. A. Smith has kindly assisted me in the examination 
of such species as are now, for the first time, brought into synonymy. 
516. IstpoRA ANGOLENSIS (Morelet). 
1866 Physa angolensis, Morel., J. de C. xiv. p. 162. D. 
1868", A » Voy. Welwitsch, Moll. p. 88. pl. 9, 
ff Be do 
1873 5,  algoensis > Sow., Conch. Icon. pl. 7, £.53. DF. 
(Err. typ.) 
1886 »» angolensis fe Cless., Conch. Cab. p. 334. pl. 47 
(1885), f.2. DF. 
Type in British Museum. 
Hab. DAMARALAND (Geale). 
Described from Angola. 
Specimens of angolensis received by the British Museum from 
Geale in 1869 were incorrectly labelled algoensis, which gave rise to 
Sowerby’s use of the latter name. Judging from the figure, 
I. parietalis (Mouss.), from Ovampoland, must be nearly allied to 
this species. It agrees in form, and the parietal plate, from which 
Mousson derived the name, is a frequent, and inconstant, feature in 
other members of the Genus. 
