PROCEEDINGS OF THE NATIONAL MUSEUM, 



VOL. 64, 



panded on anterior and posterior faces, on latter forming a shelf -like 

 overhang, that, after turning in a rounded point continues at a right 

 angle over incisura capitis to merge at the anterior end of this 

 groove with the other, more rounded, margin of the head; tuber- 

 culum inferior elevated slightly beyond level of humeral head, 

 strong, excavated slightly for a prominent triangular muscle at- 

 tachment on upper side of point, outer margin rounded below in a 

 gradually sloping obtuse angle to merge into crista inferior; in- 

 cisura capitis deep, narrow, rounded at bottom, with perpendicular 

 walls on either side; a rounded depression below humeral head; 

 distal inner margin of inferior tubercle produced over fossa subtro- 

 chanterica, the line of the margin slightly concave, the 

 external point slightly projecting; fossa subtrochan- 

 terica deep, excavated so that walls are thin, perforated 

 internally by a pneumatic foramen; outer margin of 

 crista superior slightly broken; crest sloping in a 

 slightly concave line from base of external tubercle, 

 becoming thinner, and then passing down to merge 

 with side of shaft; point of tendinal attachment elon- 

 gate, somewhat curved, with concave side outward, 

 terminating proximally at highest point of crest, end- 

 ing distally above lower end of ridge, the crest project- 

 ing at an angle of 70° with the shaft; coraco-humeral 

 groove extending at an angle across lower part of base 

 of humeral head toward outer margin of bone, shallow 

 and broad, illy defined internally, becoming impressed 

 and narrowed at incisura capitis, and terminating near 

 margin of bone below inferior tubercle, where the 

 straight walls forming it meet at the bottom in an acute 

 sharp angle; bicipital surface rounded, slightly ele- 

 vated toward upper side, limited on posterior, inner 

 margin by a slight line, but with no distinct bicipital groove,' 

 deltoid groove broad and poorly marked; lower margin of crista 

 inferior meeting shaft at a sharp, slightly obtuse, angle. 



Measurements in inlUhneters. — Length from head to nutrient 

 foramen 38.2; greatest breadth of head 15; transverse diameter of 

 shaft at nutrient foramen 4.7; distance from outer bicipital surface 

 to end of tuberculum inferior 7.7 ; 



Range. — Upper Pliocene : Known only from type locality, 2 miles 

 south of Benson, Arizona. 



Remarks. — ^In studying the present specimen I have had available 

 skeletons of the following species of the genus Dendrocygna: D. 

 autu7jmalis, D. hicolor, D. arhorea, and D. arcimta, all save arhorea 

 represented by two or more specimens. Modern tree-ducks offer so 

 many anomalies in distribution — the species Z>. hicolor for example 



Fig. 2. — Prox- 



I iM A L POR- 

 TION OF HU- 

 M B R U S 



(Type) of 

 Dendrocyg- 

 na EVEESA, 

 ANTE RIOE 



VIEW. (Nat. 



SIZE.) 



