362 PROF. ST. GEORGE MIVART ON THE 
Tae Sacro-cauDAL VERTEBRA. 
These are four in number; and the first two seem to be devoid of parapophyses, thus 
making a more or less marked distinction between them and the sacral vertebre. 
Compared with those of Phalacrocorax, they are less elongated antero-posteriorly, less 
laterally compressed as to their centra, with shorter transverse processes. 
THE CauDAL VERTEBRA. 
There are seven or eight caudal vertebra, not counting the pygostyle. They resemble 
those of Phalacrocorax; but their parapophyses are not so much bent dorsad, and are 
more dorsal at their origin in the preaxial vertebre, descending to a slightly more 
ventral origin as we proceed postaxiad. 
The pyGostyLE is even more compressed laterally than in Phalacrocorax, and thus 
differs even more than does the latter from the pygostyle of Sula. On the other hand, 
it is much more curved, like the claw of a large Felis (Plate LVIII. fig. 47). 
Tue PaLvis. 
This bony mass includes fifteen or sixteen vertebrae, extending preaxiad over the 
twenty-fifth (and sometimes even over part of the twenty-fourth) vertebra. It is very 
much less elongated, relatively as well as absolutely, than in Phalacrocorax, and is 
shorter, relatively, than even in Sula, so as to be a diminutive representation of that of 
Pelecanus as to its general proportions, though in certain details it most nearly 
approaches the pelvis of Phalacrocoras. 
Viewed laterally, the sacro-ischiatic foramen is seen to be less elongated than in Pha- 
lacrocorax, and relatively broader dorso-ventrally. ‘The union of the ilium and ischium 
postaxial to it is short, shorter than in any of the before-described genera except in 
Sula, while the ischium appears relatively deeper dorso-ventrally than in any. The 
obturator-foramen is also smaller than in any of the other forms. The ilio-caudal 
spine is long and pointed, as in Phalacrocoraa (Plate LXI. figs. 6 & 7). 
Viewed dorsally, the most striking features of the pelvis are the strong, curved 
posterior iliac ridges which bound the sacral part laterally, which part is relatively 
wider than in any preceding form save Pelecanus. These ridges absolutely distinguish 
Plotus from all the other three genera (Plate LXI. figs. 6 & 7, Ir). 
The antero-posterior length of the preacetabular part of the pelvis, as in Phalacro- 
corax, is much less, compared with that of the postacetabular part, than in Pelecanus 
or Sula; and it agrees with that of Phalacrocorax in the wing-like lateral expansion of 
its most preaxial part, and in the strong median ridge. 
The ilio-caudal spine projects postaxially little, if at all, beyond the ischium ; and the 
angle formed by it with the adjacent margin of the ischium is less acute. 
The external margin of the postaxial half of the ischium is convex, as in Phalacro- 
corax, not concave as in Sula. 
