250 Transactions. — Zoology. 



intermediate between Trihonyx and Notomis, while in others it is in advance 

 of Notomis, in just the same way as the latter is in advance of Trihonyx, i.e., 

 deviates more from normal carinate characters. 



In the shoulder-girdle the four genera form a very interesting series : this 

 is shown in fig. 6 (pi. XXI.), in which all four shoulder-girdles are reduced to 

 a common length of trunk, and the coracoids are superposed upon one another, 

 so as to coincide in direction. As regards relative length of coracoid and 

 scapula, Notornis is seen to intermediate between Ocydromiis and Porphyrio, 

 Trihonyx having the coracoid a little longer than that of Notornis, the scapula 

 somewhat shorter. The same series is observable in the curvature of the 

 scapula ; this is greatest in Porphyrio, next comes Trihonyx, then Notornis., 

 and finally Ocydromus with a scapula nearly straight save at its distal end. 



A similar gradation is seen in a more important point, namely, in the 

 angle enclosed between the adjacent portions of the coracoid and scapula. 

 As was first pointed out by Professors Huxley and Newton*, one of the 

 most marked features of the Carinatm is the fact that the coraco-scapular 

 angle never approaches 180° as in Ratita, and is usually less than 90° ; the 

 only exceptions mentioned by either author being Bicliis and Ocydromus, in 

 which the angle is slightly over 90°. This, then, is another morpho- 

 logical character which has a definite relation to the power of flight, 

 the coraco-scapular angle, like the transverse sternal angle, being found, 

 speaking generally, to increase ^jari passu with diminution of that power. 

 It would, however, be a mistake to suppose that there is anything 

 like a constant relation between flightlessness and increase of the coraco- 

 scapular angle. I find, for instance, that it is less in Tetrao than in Vultur, 

 and that of the two skeletons of Stringops in the University Museum, one 

 has the angle less than 90° on both sides, while in the other the angle on 

 the left side is just over a right angle, that on the right being the same as 

 in the other skeleton : so that the angle has undergone httle or no increase 

 in a bird in which the carina sterni is practically obsolete, and the furcula 

 rudimentary. But the strangest exception to the rule that the coraco- 

 scapular angle in the Carinatm is less than 90°, is furnished by that paragon 

 of flying birds, the albatross, in which the angle is fully 100°; the same, 

 though to a less degree, is the case in the Nelly (Ossifraga).\ Thus Dio- 

 viedea and Ossifraga must be added to the above list of exceptions, as well as 

 Stringojjs ('?), Cnemiornis, Apitornis, Trihonyx, and Notornis. As a very general 



* Huxley, " On the Classification of Birds," Proc. Zool. Soc, 1867, pp. 418 and 425 : 

 Newton, " On the Osteology of the Solitaire," Phil. Trans., 1869, p. 341, note. 



t That is, measuring by the adjacent portions of the bones only, as in the definition 

 of this angle by Huxley and Newton. Of course if the general direction of the scapula 

 be taken, the angle will be greatly diminished. I may mention, in passing, that the most 

 convenient way to take the coraco-scapular angle, is to trace the outlines of the two bones 

 on a sheet of glass held parallel to the median vertical plane of the body. 



