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Show 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 anchylosed 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 considerable 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. Shoulder-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. Bones 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 |