218 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
The sternum of Dromeus ater is remarkable, possessing as it does characters in 
common with both Caswarius and Rhea, but is at the same time Dromeine. 
As in D. nove-hollandie, the anterior lateral processes are conspicuously large and 
have the same form. The outline of the free edge of the corpus sterni from the 
articulation of the last thoracic rib backwards is the same. The coracoid grooves 
are obsolete. That of the right side is represented by a portion of the inner angle of 
the lower lip of the groove. ‘This, as is seen in the figure (4 B), persists in the form 
of a median asymmetrical tubercle. The obsolescence of these grooves indicates that 
the pectoral arch and wing were much more degenerate than in Dromeus nove- 
hollandie or D. irroratus. The corpus sterni differs from that of D. nove-hollandie in 
the relatively much greater development of the protuberantia sterni, which resembles 
that of Rhea, and in the relatively narrower width across the region of the incipient 
posterior Jateral processes. Four ribs articulate with the sternum, in D. nove- 
hollandie only three. 
The following measurements in millimetres are of interest :— 
D. nove-hollandie.  D. ater. 
(Gineeein len 6 6 6 596 5 oo - 160 95 
Greatest width (across ant. lat. proc.) . . 140 90 
Least width (across post. lat. proc.). . . 105 55 
It should be noted that the metasternum of D. ater bears traces of fracture, 
indicating a somewhat greater length than the above measurements. ‘The breadth of 
the sternum nearly equals its length. In Caswarius it is much longer than broad. 
The articular surfaces for the sternal ribs are divided one from another by pneumatic 
apertures forming pockets of great depth, extending from without inwards towards 
the middle line. The hinder border, both in Dromeus and Caswarius, is shield-shaped. 
No external lateral processes are present. The sternal plate is of great thickness and 
highly pneumatic. 
In the young Dromeus the anterior lateral processes are very short, and the ventral 
margins of the coracoid grooves are almost confluent and not separated by a deep 
median notch. 
In Casuarius the sternum is relatively much longer than in Dromeus, the increase in 
length being most noticeable from the articulation for the last thoracic rib backwards. 
The coracoid grooves are much longer, and the anterior lateral process is almost 
obsolete. In the middle line between the ventral lips of the coracoid groove in 
Casuarius there opens forward a large pneumatic aperture; this runs backwards into 
the body of the bone for some considerable distance, penetrating a low median ridge 
or protuberance resembling a vestigial keel. This is wanting in C’. wnappendiculatus, 
a shallow groove taking its place, the sides of which further back become conspicuously 
raised to form a pair of long low ridges. 
