Paekeb. — On Notornis mantelli. 251 



rule, however, a large coraco-scapnlar angle seems to be correlated with a 

 small carma sterni and large transverse sternal angle, and, taking birds of 

 the same order, there is a tolerably close relation between these structural 

 peculiarities and adaptation to a cursorial life. 



The table of comparative measurements given above shows* that, 

 arranged according to depth of carina sterni, or to size of transverse sternal 

 angle, the four genera of Rcdlidce, under consideration must be placed in the 

 following order : — 1. Forphyrio, 2. Tribonyx, 3. Notornis, 4. Ocydromus. 

 Fig. 6 shows that the same order is maintained if they are arranged by 

 the coraco-scapular angle, which is least (86°) in Forphyrio, and greatest 

 (100°) in Ocydromus, and it will be seen that the list begins with a good 

 flier (Forphyrio), and ends with a bird of purely cursorial habits (Ocydromus). 

 Similar series may be obtained by turning to other orders ; in Anseres, for 

 instance, we have 1. Anser, 2. Nesonetta, 3. Cnemiornis ; in Cohimbm, 1. 

 Columba, 2. Didus; and in Fsittacince, 1. Ara, and 2. Stringops. In all cases 

 loss of the power of flight is associated with the ratite characteristics of 

 increase of transverse sternal and coraco-scapular angles, and decrease of 

 carina. 



There is still one other point to be observed in connection with the shoulder 

 girdle : if the extremes of our ralline series be compared, i.e., Notornis or 

 Ocydromus with Forphyrio, it will be found that the forward inclination of 

 the coracoid from its sternal articulation is much less in the flightless forms 

 than in Forphyrio, in other words, that the angle enclosed between the 

 coracoid and a fore-and-aft line drawn through the coraco-scapular articula- 

 tion parallel to the long axis of the body is greater in Notornis and Ocydromus 

 than in Forphyrio. Such an angle will, of course, vary according to the 

 position of the sternum in respiration, so that its exact size is of no importance 

 and it can only be of use in the comparison of extreme forms. 



The furcula of Notornis is slender and flattened from before backwards 

 in its median portion ; this latter part is, however, very thin, so that the 

 apparent thickness of the bone in a ventral view is deceptive, and as a matter 

 of fact it is nearly as slender as in Ocydromus. As to the form of the furcula, 

 fig. 7 shows that, as in preceding cases, the four genera form an almost 

 perfect gradation, Forphyrio having the thickest and most V-shaped furcula, 

 Ocydromus the slenderest and most U-shaped. 



Felvis. 



In the characters of the pelvis the four genera no longer fall into the 

 same order, the heavy cm'sorial Notornis having a pelvis of considerably 

 greater dimensions than either of its three allies (pi. XX.) : in length, 

 in breadth, and in height the pelvis of Notornis is markedly larger than that 

 of Ocydromus, and very considerably larger than those of Tribonyx and 



* See p. 247. 



