204 MEMOIRS OF THE CARNEGIE MUSEUM 



cranium proper in the Man-o'-war-Bird might well answer for that of an Albatross 

 but slightly removed from the typical stock. Fregata, however, lacks the deep supra- 

 orbital glandular fossae so characteristic of the Diomedeidze, and, from above down- 

 wards, the skull is somewhat more compressed than it is in, for example, such a 

 species as the Short-tailed Albatross (D. albatrus) (PI. XXIX., Fig. 46). 



The superior mandible is broad at its base, and tapers gradually forwards, to be 

 armed at the apex with a powerful and decurved hook which is exceedingly sharp 

 at the point. This mandible is convex from side to side, moderately compressed, 

 and concave longitudinally along the mid-line of the culmen, from the cranium to 

 the base of the apical hook anteriorly. The narial apertures are small and situate 

 each at the bottom of a fossa-like depression, while from them running directly 

 forwards, one upon either side, is a distinct groove. It is rather deep, and very 

 narrow, not being carried upon the hooked part of the bill at its distal termination. 



No distinct cranio-facial hinge exists, but at the middle point in that region 

 the proximal ends of the premaxillaries remain unobliterated throughout life (PI. 

 XXIX., Fig. 46). 



Deeply concave towards each other, and with sharpened margins, the superior 

 borders of the orbits are separated from each other by an interval of something 

 more than 2 cm. Mesially, the intervening frontal surface shows a slight eleva- 

 tion, while in the parietal or post-frontal region there are two larger, convex and 

 elongated elevations placed side by side with a median, not at all deep, depres- 

 sion passing between them. Within the cranial casket these elevations harbor the 

 superior surfaces of the cerebral hemispheres, and the skull is thinner there than 

 elsewhere (PI. XXIX., Fig. 46). 



The crotaphyte fossse are well-defined, even better so than in an Albatross (D. 

 albatrus), being very slightly depressed below the general surface, and, in the mid- 

 dle line posteriorly, do not meet by an interval of a centimeter (PI. XXIX., Fig. 45). 



Apart from this character, and the fact that the squamosal processes are more 

 prominent and sharper in Fregata, the posterior aspect of its cranium agrees almost 

 exactly, character for character, with what is presented to us on that view in the 

 cranium of D. albatrus. In this I do not exclude the pterygoids and quadrates. 



The large subvertical, subcylindrical foramen magnum is partially overarched 

 by the well-defined occipital area, and the condyle, although of the same shape, is 

 not quite as prominent as it is in an Albatross (PL XXIX., Fig. 48). 



Seen upon side view, we are to note the deep valley of the temporal fossa, made 

 so by the large outstanding post-frontal process anteriorly and the sharp, ridge-like 

 squamosal projection referred to above (PI. XXIX., Fig. 45). 



