STRIGIDJS — THE OWLS. 5 



contour. As a rule, we find that those skulls which have the greatest 

 pneumaticity (e. g. Strijc and Otus) are niost depressed anteriorly, have the 

 orbital septum thicker, the palatines longer and narrower, and a deeper lon- 

 gitudinal median valley on the superior surface, and vice versa. 



The following classification is based chiefiy upon external characters ; but 

 these are in most instances known to be accompanied by osteological pecu- 

 liarities, which point to nearly the same arrangement. It is intended merely 

 as an artificial taljle of tlie North American genera, and may be subjected 

 to considerable modification in its plan if exotic genera are introduced.^ 



Genera and Subgenera. 



A. Inner toe equal to the middle in length ; inner edge of middle claw 

 pectinated. First quill long-er than the third ; all the quills with their inner webs 

 entire, or without emargination. Tail emarginated. Feathers of the posterior 

 face of the tarsus recurved, or pointed upwards. 



1. Strix. No ear-tufts; bill light-colored ; eyes black ; tarsus 

 nearly twice as long as middle toe; toes scantily haired. Size 

 medium. Ear-conch nearly as long as the height of the skull, 

 with an anterior operculum for only a portion of its length; 

 symmetrical. 



B. Inner toe decidedly or much shorter than the middle ; inner edge of middle 

 claw not pectinated. First quill shorter than the third ; one to six outer quills 

 with their inner webs emarginated. Tail rounded. Feathers of the posterior 

 face of the tarsus not recurved Ijut pointed downwards. 



I. Nostril open, oval, situated in the anterior edge of the cere, which is not 



inflated. 



a. Cere, on top, equal to, or exceeding, the chord of the culmen ; much 

 arched. Ear-conch nearly as long as the height of the skull, with the 

 operculum extending its full length ; asymmetrical. 



2. Otus. One or two outer quills with their inner webs 

 emarginated. With or without ear-tufts. Bill blackish ; iris 

 yellow. Size medium. 



Ear-tufts well developed ; only one quill emarginated . Otus. 

 Ear-tufts rudimentary ; two quills emarginated . Brachyotus. 

 h. Cere, on top, less than the chord of the culmen ; gradually ascending 

 basally, or level (not arched). Ear-conch nearly the height of the skull, 

 with the operculum extending only a part of its full length, or wanting 

 entirely. 



t Anterior edge of the ear-conch with an operculum; the two ears 

 asymmetrical. 



3. Syrnium. Five to six outer quills with their inner 

 webs emarginated. Top of cere more than half the culmen. 

 Without ear-tufts. Bill yellow ; iris yellow or black. Size 

 medium or large. 



Six quills emarginated ; toes densely feathered, the ter- 

 minal scntelte concealed; iris yellow. Size very large Scotiaptex. 



My unpublished determinations of the North American species were furnished, by request, 

 to Dr. Cones, for introduction into his -'Key of North American Birds"; consequently the 

 names used in these pages are essentially the same as those there employed. 



