108 DR. R. O. CUNNINGHAM ON RHEA. [Feb. /, 



of immaturity of development, but also, I am inclined to believe, 

 from more prolonged maceration. 



Pelvis. — On comparing the pelves of the two birds it will be noticed 

 that in R. americana the transverse processes of two vertebrae abut 

 upon the iliac bone of either side, opposite its junction with the 

 ischium and pubis ; while in R. darwinii the transverse process of 

 but one vertebra occupies this position, and this process is much 

 shorter than the corresponding processes in R. americana, so that 

 the acetabula of opposite sides are further removed from one another 

 in that bird than in R. darwinii. In the specimen of the latter 

 bird, owing to its youth, the ischiatic and pubic bones, though an- 

 chylosed to one another, are not yet anchylosed to the ilium, while 

 in the older specimen of R. americana they are firmly anchylosed, 

 although still presenting indications of the line of junction. A con- 

 siderable difference, perhaps due in part to age, obtains between the 

 posterior extremities of the ischium and pubis in the two birds. In 

 R. darwinii they are separated by a considerable space, while in 

 R. americana they are nearly in contact, owing to the development 

 downwards and forwards of a strong process from the ischium. 



Shoidder-girdle. — In the specimen of R. americana the coracoid 

 and scapula are anchylosed, while in that of R. darwinii they are 

 separate. In the former the strong internal process at the scapular 

 end of the coracoid is much more developed than in the latter ; and 

 the inner border of the sternal extremity of the same bone is of a 

 different form in the two birds, in R. americana being as it were cut 

 away for the space of about a quarter of an inch, while in R. darwniii 

 it presents a convex curve. A strong rounded process occurs at 

 the proximal extremity of the scapula, at about the middle of its 

 antero-inferior surface in R. americana, and is but feebly indicated 

 in R. darwinii. 



Bones of the Wing. — The humerus, radius, and ulna of the two 

 birds present no conspicuous differences, save those of size. I have 

 been unable to institute a comparison between the carpal bones of the 

 two species, as they are incomplete in the skeleton of R. americana 

 and missing in that of R. darwinii. In the former the os magnum is 

 anchylosed to the proximal ends of the second and third metacarpals, 

 and all three metacarpals are partially anchylosed ; while in the latter 

 the os magnum is unanchylosed (missing), and all three metacarpals 

 are as yet ununited. These latter bones closely resemble each other 

 in form in both birds, with the exception that in the specimen of 

 R. americana they are much more curved than in R. darwinii. 

 This difference may possibly, however, be of an individual, not of a 

 specific nature. The digits are incomplete in both skeletons, so that 

 they could not be compared. 



Rones of the Leg. — The general form of the femur is the same in 

 both skeletons ; but the intercondyloid fossa is much deeper in R. 

 darwinii than in R. americana, and is due probably to its youthful 

 condition. The various elevations and depressions on the shaft of 

 the bone, indicative of the origin and insertion of muscles, are, as 

 might be expected, more distinctly marked in the latter species. In 

 the tibia of R. americana a strong procnemial ridge is developed from 



