468 TEST ACE A ATLANTIC A. 



Habitat Lanzarotam, Fuerteventuram, Canariam Grandem, 

 Teneriffam, Gomeram, et Palmam ; in Hierro sola adhuc haud 

 inventa. 



The common European P. acuta^ which has been introduced 

 into the freshwater tanks of Madeira, occurs almost universally 

 (if not indeed quite so) in the Canarian Group, Hierro being 

 the only island out of the seven where it does not happen 

 hitherto to have been observed. Indeed I have myself taken 

 it in Lanzarote, Fuerteventura, Grand Canary, Teneriffe, and 

 Palma ; and it was obtained in Gomera by Fritsch. 



The P. acuta is, on the average, rather smaller and 

 slenderer at the Canaries than in more northern latitudes, and 

 the examples vaiy a little according to the exact locality, and 

 island, in which they are found ; but, judging from an immense 

 series to which I have access, I cannot detect anything about 

 them to induce me to think that they are specifically distinct, 

 or that they represent anything more than one or two very 

 slight and unimportant insular modifications of the variable 

 European shell. I do not therefore agree with Mousson in 

 considering it desirable to erect them into an additional species 

 under the title of P. tenerifce, believing, as I do, that we are 

 already burdened with far too many ' species,' so-called, elabo- 

 rated out of the mere geographical aspects of these eminently 

 inconstant members of the Limnceidce. And I would even 

 advance a step further and suggest that the somewhat larger 

 and more inflated Physa which (although admitted by its 

 original describer, Moquin Tandon, to be but a race of the P. 

 acuta) is likewise upheld by Mousson as yet another exponent 

 of the genus (under the name of P. ventricosa\ and which is 

 said to occur in the ' Environs [!] de Tenerife ' (whatsoever 

 that may mean), itself disproves the assertion that the Canarian 

 species is uniformly smaller than the European one ; the real 

 fact being that only selected examples of it are smaller, 

 occasional ones being quite as much enlarged as those which are 

 commonly found in Europe, or as those from Madeira. Indeed 

 Mousson himself, even whilst enunciating the k P. tenerifoe' 

 and a number of (supposed) subordinate varieties, was evidently 

 uneasy as to its real specific claims, for he expressly speaks of 

 its 'affinite avec certaines petites formes francaise de la P. 

 acuta. 9 



My Lanzarotan examples of this Physa were taken in the 

 Lake Januvio, on the western coast of that island ; the Fuerte- 

 venturan ones in the Rio Palmas ; the Grand-Canarian ones 

 in the district of El Monte ; and the Teneriffan ones near 

 Laguua. 



