BIRDS OF NOETH AND MIDDLE AMERICA. 597 



claws. Even in the character of the bill and feet, however, the 

 resemblance is largely a superficial one, and when a close examination 

 is made many constant differences become obvious in the structural 

 details of the bill and feet m the two groups. Thus in the Striges the 

 maxillar tomium is never notched, toothed, nor lobed; the "cere" is 

 of very different character, consisting, in reality, of the usual mem- 

 brane covering the unperf orated part of the nasal fossa?, contiimed 

 across the mesorinal portion of the culmen, the so-called cere being 

 thus wholly post- and supra-nasal, usually with the lateral (post- or 

 circum-nasal) portion more or less inflated. It is in. the structure of 

 the feet, however, that the greatest difference is observable. 



"The structure of the feet and more particularly the toes of owls is 

 very peculiar. When perching, the arrangement of the toes is zygo- 

 dactyl; that is, two in front and two behind, ** but when an owl pounces 

 upon its prey, the four toes point to the four quarters of a circle. 

 Again, when the bird alights upon the ground, the arrangement is 

 still different, being more like that of a tjrpically avian foot — three 

 toes in front and one behind. This facile adjustment to different 

 conditions makes the foot of great efficiency in all its functions." ^ 

 A single member of the Accipitres, the genus Pandion, "shares the 

 digital elasticity of the owls," and also, alone in that order, possesses 

 the bony tarsal ring or loop, a character evidently correlated with the 

 digital manipulation. 



The following special papers pertaining to the structure and classi- 

 fication of owls are commended to those who desire further informa- 

 tion on the subject: 



CoLLETT, Robert. ^ — Craniets og Oreaabningemes Bygning hos de nordeiiropaeiske 

 Arter af Familien Strigidse. 



An English translation edited and annotated by Dr. R. W. Shufeldt was pub- 

 lished in the Journal of Morphology, xvii, 1900, 119-17G, pis. 15-20+7 text cuts, 

 vmder the title "Professor Collett on the Morphology of the Cranium and the 

 Auricular Openings of the North-European species of the Family Strigidse," the 

 illustrations from the original paper. 



Clark, Hubert Lyman. — The Pterylography of certain American Goatsuckera and 

 Owls. Proc. U. S. Nat. Mus., xvii, no. 1018, 1895, 551-572; 11 cuts in text. (Owla 

 treated on pp. 559-566, a key to the genera, based on pterylographical characters 

 alone, being given on p. 560.) 



Ptcrapt, W. p. — A Contribution toward our Knowledge of the Morphology of the 

 Owls. Trans. Linn. Soc, 2d ser., Zool., vii, 1898, 223-275, pis. 24-29. 



Pycraft, W. p.— On the Pterylography of Photodilus. The Ibis, Jan., 1903, 36-48, 

 pi. 2; 6 cuts in text. (Includes a "Revised Key to the Subfamilies and Genera 

 of the Family Asionidse, " on pp. 47, 48.) 



Beebe, C. William.— Owls of the Nearctic Region. Reprinted from the Eleventh 

 Annual Report of the New York Zoological Society. Pp. 38, 1 full-page (frontis- 

 piece) and 15 text cuts, all reproduced from photographs. (1907.) 



a This is not strictly correct, for when perching the outer toe usually stands nearly 

 at right angles with the middle toe and hallux, though often inclined more h>u;k- 

 ward than forward. 



f> Beebe: Owls of the Nearctic Region, p. 11 



