272 TEST ACE A ATLANTIC A. 



from 1 to 4), and by its ventral 'paries being not un frequently 

 armed with an extra plait or tubercle, — i.e. with three, instead 

 of two. Still, this additional callosity, last-mentioned, is more 

 often absent ; and in that case, if the right margin of the 

 peristome should happen at the same time to be unprovided 

 with denticles, and the specimens to be large ones, the latter 

 would be difficult to distinguish, no doubt, from those of the 

 A. Watsoni ; but as I have never yet observed this threefold 

 contingency to take place, there is no reason why we should 

 assume it to do so at all. 



The A. gracilis occurs sparingly adhering to the tide- 

 washed rocks in Madeira proper, but it appears to be more 

 common in the north of the island than in the south. Mr. 

 Lowe's original examples, however, were found (dead), during 

 February of 1827, on the shore to the westward of Funchal. 

 By the Baron Paiva it has been obtained from Porto Moniz. 

 It is recorded by both Morelet and Drouet from Pico, in the 

 Azorean archipelago ; but I am not aware that it has been 

 observed hitherto at the Canaries. 



Fam. 6. LIMNJEIDJE. 



Genus 18. LIMNJEA, Drap. 



\scrij)t. Limneus.] 



Limnsea truncatula. 



Buccineum truncatulum, Mull., Verm. Hist. ii. 130 (1774) 

 Limneus minutus, Drop., Hist. Nat. 53. t. 3. f. 5-7 (1805) 

 Limnoeus truncatulus, Lowe, Proc. Zool. Soc. Load. 218 



(1854) 

 Limnoea truncatula, Paiva, Mon. Moll. Mad. 146 (1867) 

 „ „ Watson, Joam. de Conch. 22 i (1876) 



Habitat Maderam ; in aquis fiuentibus et quietis, necnon ad 

 rupes aquosas, ubique vulgaris. 



The common little European L. truncatula, Mull. ( = L. 

 minuta, Drap.), abounds in nearly all the streams and Levadas 

 of Madeira proper, but it has not yet been observed in any of 

 the other islands. It occurs independently of elevation, par- 

 ticularly within the douche of the waterfalls, and is very variable 

 in stature. The Madeiran specimens however are perhaps, on 

 the average, a trifle smaller than those on the more ordinary 

 northern type. We did not meet with it at the Canaries, nor 

 indeed is it recorded by Mousson from that archipelago ; but it 

 is nevertheless registered as Canarian by Mr. Watson. 



