250 Mr. Forbes on the Land and Freshwater 



is a little more in proportion to the white, and in some indi- 

 viduals the bill is furnished with two processes in the upper 

 mandible, like the young of the preceding species, except that 

 the bars on the two middle feathers in the tail are continuous. 



Note. — The day after the above paper w^as read, two 

 mature specimens were received from Iceland ; they are male 

 and female, and have just come through the moult, and cor- 

 respond exactly in the markings with the breeding individuals 

 brought by Mr. Proctor ; they are, however, a little brighter 

 in colour, occasioned principally by the freshness of the plu- 

 mage, and certainly do not vary more than might be expected 

 from the difference in the young from the same nest. I may 

 also observe that all the mature specimens I have seen from 

 Iceland, amounting to seven in number, have the upper man- 

 dible furnished with two processes ; whilst in the many Green- 

 land specimens I have examined, only two have had the dou- 

 ble process, and these were apparently very old individuals. 



EXPLANATION OF THE PLATE. 



A. Tail-feather of young Falco Islandicus. B. Primary of mature ditto. 

 D. Lesser wing-covert feather of ditto. 



E. Primary of mature Falco Groenlandicus. F. Tail-feather of young 

 ditto. G. Covert feathers of mature ditto. 



XXVIII. — On the Land and Freshwater Mollusca of Algiers 

 and Bougia. By Edward Forbes. 



[With Plates*.] 



During a visit to the regency of Algiers in May 1837^ I ob- 

 tained forty-five species of land and freshwater Mollusca, chiefly 

 collected in the neighbourhoood of the city of Algiers and of 

 the town of Bougia (in the province of Constantine). M. Mi- 

 chaud, a distinguished French naturalist, published the year 

 before a pamphlet entitled, ' Catalogue des Testaces vivans 

 envoy^s d' Alger, par M. Rozet,' in which he enumerates 

 twenty-five species of land and freshwater shells ; but a great 

 part of these are not correctly speaking from Algiers, but from 

 Oran (near Morocco), m here the Fauna of Barbary assumes a 

 different aspect, approximating to that of the Canaries on the 

 one hand, and to that of Spain on the other. 



* These plates will form part of the Supplement. 



