No. I.] NORTH AMERICAN PASSERES. 87 
Feebleness of structure seems to characterize its mandzble, or 
rather that bone throughout the genus; it being of the typical 
V-shape pattern, with shallow ramal sides, having rounded upper 
and lower margins; a conspicuous, sub-elliptical ramal vacuity 
on either side ; while the bone as a whole shows a slight though 
abrupt flexure downwards just beyond its middle. As for the 
symphysis, it is short, convexed below, concaved above; and at 
each hinder extremity the articular cup develops a posterior-pro- 
jecting process, which is directed slightly upwards. 
Taking aspecimen of Sza/za arctica as an example, we find that 
in its vertebral column there are 19 vertebrz included between 
the skull and the pelvis; of these, the first twelve are without 
free ribs, —the leading minute pair of riblets occurring on the 
thirteenth vertebra. On the fourteenth vertebra, the pair of 
ribs, although not connecting with the sternum, are much better 
developed, and may possess uncinate processes. The last five 
free vertebrae of the spinal column are true “dorsals,” if we may 
so nominate vertebrae which support vertebral ribs, that not only 
have uncinate processes, but connect through hzmapophyses 
with the sternum, as these all do. There is also a delicate pair 
of sacral ribs, which usually are devoid of processes, and whose 
hamapophyses fail to reach the costal borders of the sternum. 
Upon examining specimens of Merula, Turdus, and Myadestes, 
as well as the Varied Robin (4. x@vza), I find that they all cor- 
respond in this particular with Sza/za, both as to number of ver- 
tebrze, the ribs, and their epipleural appendages. Doubtless it is 
the formula for all true 7uraide. 
Bluebirds have rather a shallow fe/vzs, short in the antero- 
posterior direction, and with the hind ends of the post-pubis 
and ischium, on either side, inclined to flare outwards. The ilia 
are never in contact with each other; quite the reverse, for the 
groove upon each side of the sacral crista in front is wide, caus- 
ing the total interval in this region to be quite considerable. In 
mid-postacetabular space we always find the double row of parial 
1 Since the above was written, an excellent paper has appeared from the pen of 
Mr. F. A. Lucas, entitled ‘Notes on the Osteology of the Thrushes, Miminz, and 
Wrens” (Proc. U. S. Nat. Mus., 1888, pp. 173-180). It not only contains much 
osteological information on the groups treated, but is illustrated by a number of 
useful outline figures, that may well be compared with what we have to say further 
along, 
