218 MEMOIRS OF THE CARNEGIE MUSEUM 



illustrating this memoir (Plate IV., Figs. 13-21 and Plate VI., Figs. 25, 27 and 29). 

 They not only vary in size according to the species, but perhaps the most interest- 

 ing variation they offer is the marked vertical compression of the skull they exhibit, 

 associated, as it is, with a decided elongation and narrowness of that part of the 

 skeleton. This is well seen in such a species as Phalacrocorax pelagicus robustus, where 

 this character about reaches its maximum. At the other extreme, we find the skull 

 of some Cormorants to be moderately shortened, with a broad, dome-like cranium, 

 .which admits of an unusually capacious brain cavity. A species having this char- 

 acter markedly exemplified is Phalacrocorax albiventris, and its skull is shown in 

 Plate IV., Figs. 14 and 21, and in Plate VI., Fig. 29. A good medium type stand- 

 ing between these two extremes is seen in Phalacrocorax dilophus, while all the other 

 species of Cormorants tend either toward P. p. robustus, or toward P. albiventris in the 

 matter of this flatness and elongate-narrowness of their skulls, or in the shorter, 

 broader and more capacious cranium of the last-named species. The shading either 

 way is often so gradual that everything else being equal, it hardly seems to offer 

 justifiable grounds for generic divisions. Associated with these forms of the skull 

 in the Cormorants, we are to note the variation in the form of the pterygoid bones 

 at the inferior aspects of the same. Some Phalacrocoracidse possess long and com- 

 paratively slender pterygoids, while other species have them much shorter and 

 stouter. Phalacrocorax p. robustus is an excellent example of the first of these (Plate 

 VI., Fig. 28), while P. albiventris well exhibits the last-named condition, while in 

 P. dilophus again, they are moderately elongated and fairly stout, thus once more, 

 affording an example of the medium type in this particular. In some Cormorants 

 the mesethmoid bone is not perforated by a large median vacuity, as is seen to be 

 the case in others. It is thus perforated in such species as P. p. robustus and P. albi- 

 ventris, while it is perfectly solid in such forms as P. dilophus and P. melanolcucus. 

 There are also interesting differences to be noted in the comparative size and form 

 of the foramen magnum, the morphology of the cranio-facial hinge, and other 

 minor points, the majority, of which, if of any importance, are noticed in the body 

 of the present memoir. 



The pelvis in the various species of the Cormorants also exhibits a difference in 

 form. In P. pelagicus, for example, it is comparatively short, narrow, and with the 

 ilio-ischiatic notch not very deep, while in Graculus Carbo, it is much elongated, 

 narrow, and the aforesaid notch very deep. Other species of the Phalacrocoracidse 

 tend one way or the other in this particular. The short-bodied Cormorants have 

 the sternum more or less broad and short, while in the long-bodied species this bone 

 is likewise more elongated and narrower. 



