XIV, 1 Shufeldt: Osteology of Porphyria 99 
Museum) and those of Colymbus cornuttis (No. 17873, United 
States National Museum). 
Taken as a whole, the skull of Tachybaptus agrees much 
better with the skull of Colymbus than it does with that of 
Podilymbus — a fact due principally to the shortening and broad- 
ening of the superior mandible and jaw in the latter form. The 
space between the superior peripheries of the orbits in the 
frontal region is quite as broad in the Philippine grebe as in 
the dabchick, while in the horned grebe it is much narrower. 
Tachybaptus presents a peculiar character in the pterygoids 
not to be found in the skulls of tl^e two species with which it 
is here being compared ; this consists in their being, in the case 
of either pterygoid, gradually broadened out by thin laminse 
that pass from the quadrate end to the palatine of the same 
side, the broadest part being the distal third. In Colymbiis 
these bones are very slender rods, with scarcely a trace of laminar 
expansion. 
The hyoid arches seem to have been lost in these skeletons 
except in Tachybaptus, where they have been preserved with 
the trachea. The glossohyal is rather short and broad, the 
urohyal being very slender. The hypobranchials are long, and 
the ceratobranchials very short, while the two together are 
reduced almost to hairlike proportions, so exceedingly slender 
are they in caliber. 
Throughout its length the trachea is simple in structure, and 
the numerous rings are entire and thoroughly ossified from first 
to last. ' 
The true grebes seem to possess eighteen cervical vertebrae 
in the spinal column to seventeen of Podilymbus ; possibly one 
may have been lost in the skeleton of the latter bird at hand, 
but I am inclined to think not. 
Tachybaptus has the first pair of ribs on the nineteenth ver- 
tebra; they are without costal ribs, though the epipleural ap- 
pendages are well developed and long. These do not ankylose 
with their ribs anywhere in the series, and they are found upon 
the next following four pairs of ribs, all of which latter have 
true costal ribs. There are two pairs of pelvic ribs; the first 
pair reaches the sternum through costal ribs, while the second 
does not. Behind these a very delicate pair of floating hsema- 
pophyses is seen. None of these possess unciform appendages. 
We find the same arrangement in Podilymbus podiceps, while 
in Colymbus coimutus there are nine pairs of ribs, the leading 
seven pairs having unciform processes. The first two pairs do 
not possess costal ribs ; and the last two pairs, which are pelvic 
