THE NAUTILUS. 113 



Rhine. But now Dr. C. R. Boe.ttger 1 described a new variety of 

 Physa actua from Oppeln in Silesia, which he calls var. thermalis. 

 It is said to differ from the type by its larger size, thicker shell and 

 irregular surface. In the same locality lives a species of Spf/arium, 

 which is described as Sph. tetensi sp. n., but the author says that it 

 is quite similar to the American Sph. simile Say. From the illus- 

 tration of the new variety of Physa acuta it is evident that there is 

 no acuta at all, but that this form is quite identical with the large 

 specimens of Physa heterostropha, which occurs near Prague of the 

 same size. How the case stands with other records from Central 

 Europe, I dare not say ; but it is very probable that all these sup- 

 posed Physa acuta are in reality P. heterostropha, which was intro- 

 duced with American fishes and plants of aquaristic commerce, and 

 which found in our waters suitable circumstances of life. On the 

 contrary Physa acuta as an animal of warmer regions of Western 

 Europe scarcely could live any long time in the cold waters of our 

 pools and brooks. 



NOTES ON THE ANCYLIDAE OF NORTH AFEICA. 



BY BRYANT WALKER SC. D. 



Through the great courtesy of M. Paul Pallary of Oran-Eckmuhl, 

 Algeria, the well-known student of North African Mollusca, I have 

 been recently enabled to study his entire collection of North African 

 Ancylidce. 



The collection consists of twenty-nine lots, nineteen from Algeria, 

 six from Morocco, one from Tunis and four from Egypt. 



In preparing the following notes, which are based mainly on M. 

 Pallary's collection, I have made, use of such additional material as 

 I have in my own collection and such of the literature as I have at 

 my disposal. 



I am under special obligations to Dr. E. F. Weber of the Natural 

 History Museum of Geneva, Switzerland, for drawings and inval- 



1 C. R. Boettger, Beitrage zur Kenntniss der Molluskenfauna Schlesiens. 

 Nachrbl. d. deutschen Malakozool. Ges., 1913. 



