264 PKOFESSOE OWEN ON CNEMIOENIS. 



rounded angles, retaining a breadth of 3 inches 3 lines at this end, which is devoid of 

 the pair of notches characterizing, as a rule, the Anserine sternum '. 



Cnemiornis follows the rule of keelless, or rudimentally keeled, breast-bones of 

 flightless fowl in the integrity of the bony shield. The length of each coracoid groove 

 is 1 inch 6 lines, the greatest depth 1| line. From near the lateral end of the outer 

 wall the pectoral ridges extend backward, slightly converging, but cease to be traceable 

 after a course of 2 inches. The costal process {d) is quadrate, relatively thicker and 

 more produced than in Cereopsis or Tachyeres. The outer surface, defined by a low 

 curved ridge, is so smooth as to have suggested the remark at p. 399, Trans. Zool. Soc. 

 vol. V. The inner surface of the base of both right and left of these processes shows a 

 large reticulate pneumatic vacuity. 



The costal border indicates the same degree of longitudinal curve, convex outward, of 

 the coextensive part of the breast-bone as in Cereopsis ; but is relatively more extensive, 

 and is traversed obliquely from within outward and backward by seven articular promi- 

 nences for the sternal ribs. The five anterior of these are ridges expanded at the ends 

 into articular tubercles ; the sixth and seventh are represented by the inner tubercle 

 only. A smaller tubercle (ib. fig. 3, h l), in advance of the broad ridges, may afford 

 attachment to the haemapophysis of the second free rib. The breadth of this surface is 

 shown in fig. 3. Cereopsis has but five articular prominences on each costal border. 

 Tachyeres has seven, as in Cnemiornis. The outer surface of the sternum near the 

 costal border is feebly concave transversely, before swelling into the convexity producing 

 the hollow cavity of the anterior half of that bone next the thoracic abdominal cavity. 



It would seem that a comparison with the view of tracing affinity within the limits 

 of the Lamellirostaal group could not profitably be made between the almost keel- 

 less breast-bone of Cnemiornis and the deeply keeled ones in all existing members of 

 such gi'oup ; for even the sternum of the flightless Steamer-Duck has " the great 

 development of the keel " which the experienced ornithologist Eyton adds to his 

 osteological characters of the family Anatidse I However, there is a greater convex 

 curve of the free border of the sternum in Cereopsis^ than in Anser cygnoides^ or in 

 Tachyeres ; and, in a small degree, this approximates Tachyeres and Cereopsis to Ciconia. 



§ 5. lAml-Bones. 

 The coracoid (PI. XXXVII. figs. 4-7) accompanying the collection of Cnemiornis bones 

 now described, is of the left side, and wants only the terminal expansion fitting to the 



' Eyton, ' Monograph on the Anatidae,' 4to, 1838, pi. 1. figs. 7-11. ClcmguU (fig. 4) and FaUgida (fig. 5) 

 agree with the Goosander {Merr/us serrator) in the conversion of these notches into foramina. Cereopsis and 

 Tachyeres adhere to the anseiiue type. 



' Eyton, in his classical Monograph (4to, 1838, p. 5), follows Vigors in making " Anatida; " (which suggests 

 rather the tribe or subfamily of Ducks) the equivalent of Cuvier's well-conceived term " LameUirostres." 



' Id. Supplement to ' Ostoologia Avium ' (4to, 1869), pi. ii. Cereopsis. ' Ib. pi. 3. 



