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 was 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 Grcenlandicus. 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, i Catalogue des Testaces vivans 

 envoyes d 5 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), where 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. 



