122 



It differs from Ayl. Brasiliensis by its smaller size and more deli- 

 cate bill ; the greenish tinge of the blue is much more extended, as it 

 invades the whole of the head and tail-coverts as well as the inte- 

 rior of the wing. 



19. Aglaia ScHRANKii, Nob. A.viridisnigromaculata,uropy- 

 gio et medio corpore subtus luteo-aureis : f route genisque nigris : 

 remigibus rectricibusque fuscis externe cyaneo marginatis. 



Tanagra Schrankii, Spix, tab. 51, fig. 1 and 2. D'Orbign., pi. 

 24, fig. 1. 



Closely resembling Agl. punctata, Edw., pi. 262, but differs in 

 having the rump, and the middle of the body underneath golden 

 yellow, and without spots. 



20. PiPRA STRioLATA, Nob. P. oUvacea, subtus rufa, albo stri- 

 ata: pileo cristato coccineo. 



Exceedingly like the Pipra strigilata of the Prince Max. of Wied, 

 from Brazil, but sufficiently distinguished by the under parts being 

 rufescent striped with white, instead of white striped with rufous. 

 Wagler describes, however, my species. 



Mr. Blyth exhibited some portion of the skeleton of the Great 

 Auk, Alca impennis, and proceeded to offer some observations on the 

 distinctions subsisting between the Auks and the Penguins. He 

 remarked that these two genera differ in the type of their skeleton 

 as well as in the progressive changes and structure of their plumage, 

 for which reason he had long wished to obtain a sight of the skele- 

 ton of the Alca impennis, with a view to ascertain to what extent the 

 similarity of its mode of life to that of the Penguins would, in this 

 species, modify the Auk type of structure. Through the kindness 

 of his friend Mr. Bartlett, he had succeeded in obtaining the wing 

 and leg bones of this remarkable bird, which had been left in a pre- 

 served skin, and which proved to resemble those of the Penguin 

 genus in weightiness, if not in structure, the humerus possessing a 

 very small internal cavity, while the tibia was completely filled with 

 marrow. These bones were exhibited, together with the analogous 

 bones of Alca tarda, which latter were even proportionally consider- 

 ably smaller, as well as lighter, and quite hollow. Mr. Blyth re- 

 marked that the gradual absorption of the marrow in the bones of 

 other birds was about coincident with the developement of the volar 

 organs ; and stated the highly curious fact, on the authority of Mr. 

 Gould, that the marrow was permanent in the leg bones of the genus 

 Cinclus. He then made various observations on the structure of the 

 northern or true Alcadcs, more particularly with relation to the de- 

 velopement of the air-cavities in the species which could sustain 

 themselves on wing, observing, that in these the wings were reduced 

 to the minimum extent adequate for aerial support, in order that 

 they might be more effectual under water ; and that when once tlie 

 object of aerial flight was abandoned, as in the instances of the great 

 Auk and Penguins, these organs were accordingly reduced to exactly 



