8 Ridgway American Families of Oligomyodian Passer es. 



TRACHEOPHON.E.* 



A. Sternum with one pair of posterior notches. 



a. Tarsus endaspidean 1. Dendrocolaptidae. j 



6. Tarsus taxaspidean ----- 2. Formicariidit. 



B. Sternum with two pairs of posterior notches. 



a. Tarsus exaspidean 3. Conopophagidae. 

 6. Tarsus taxaspidean - - 4. Pteroptochidae. 



It is thus seen that the character of the tarsal envelope is Dr. 

 Sclater's chief reliance in the discrimination of these groups. 

 This character is undoubtedly one of considerable importance, 

 probably the most important of any single external character ; 

 but unfortunately when carefully tested it does not work out so 

 beautifully as would appear from Dr. Sclater's presentation of 

 the case. If it did, certain genera referred by him to the 

 Tyrannidse would belong to the Cotingidre, while a considerable 

 number of genera referred by him to the latter group could not 

 be placed at all, since their tarsal envelope is neither exaspidean, 

 pycnaspidean, taxaspidean, nor ocreate. It is evident, there 

 fore, that a really "workable" key must be based on other 

 characters in addition to that of the tarsal envelope. An effort 

 to devise a satisfactory one has engaged a considerable amount 

 of my time; but, while I believe that some improvement has 

 been made, I must confess that it does not wholly satisfy me, 

 and the results are herewith presented only as a provisional class 

 ification, with the observation that a really natural one is 

 scarcely possible until the internal structure of all the genera has 

 been studied. 



PROVISIONAL KEY TO THE FAMILIES OF MESOMYODI. 

 a. Syrinx broncho-tracheal (typically Passerine). (Oligomyodi.) 



b. Syringeal muscles anachromyodous ; tarsal envelope exaspidean; 



middle toe coherent with outer toe for not more (usually less) than 

 the whole length of its basal phalanx, 

 c. Bill cuneate, its tip acute and not at all uncinate, 



1. Oxyruncidae. 

 cc. Bill not cuneate nor acute, its tip more or less uncinate. 



2. Tyrannidae. 



bb. Syringeal muscles catacromyodous ; tarsal envelope not exaspidean, 

 or else (Pipridse) the middle toe coherent with outer toe for more 

 than its basal phalanx or (genus ,Pipreola of Pipridse) coherent 

 with inner toe for whole of its basal phalanx, 

 c. Temporal fossae normally Passerine. 



d. Intrinsic muscles normally catacromyodous ; tongue not penicil- 

 late. 



* Cat. Birds Brit. Mus., xv, 1890, 2. 



t The Dendrocolaptidae of Dr. Sclater includes the very distinct family Furnariidse. 



