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Show 1042 MR. W. P. PVCRAFT ON THE [Dec. 19, families; Dr. Gadow would regard these as of subordinal value. Which of the two views will become ultimately adopted remains to be seen. Probably the first is a sufficiently wide separation. Finally,-and it had almost escaped mention,-the skeleton of the Pygopodes is non-pneumatic. xi. K E Y TO THE OSTEOLOGY OF T H E PYGOPODES. A. SKULL. (Plate LXXII.) Holorhinal and schizognathous; nares pervious ; vomer cleft posteriorly; basipterygoid processes absent; lachrymal small, feebly developed, not extending downwards to join the quadrato-jugal bar; quadrate with an elongate orbital process; maxillo-palatine processes in the form of horizontal laminae, never extending as far backwards as the scroll-like antero-internal border of the palatine; basitemporal plate of the parasphenoid with an inflated anterior border converting the Eustachian grooves into tubes, with a median aperture below the parasphenoidal rostrum ; temporal fossae more or less well developed. Dentary suture of mandible tending to disappear in the adult. Angulare truncated. A. Supraorbital grooves very deep, with a well-developed ledge; temporal fossae wide, separated one from another superiorly by a median sagittal ridge; lachrymal more or less completely fused with the nasal; vomer grooved and laterally expanded dorsally ; with a deep median, ventral keel, and with a strongly marked ventral keel in front of the parasphenoidal rostrum ; Eustachian grooves never completely closed ; large postorbital and paroccipital processes COICYMBIDCE. (Only one genus-Colymbus.) B. Supraorbital grooves feebly developed or absent ; lachrymal free, not projecting posteriorly from the sides of the supraorbital margin ; vomer blade-shaped ; Eustachian grooves completely closed ; postorbital and paroccipital processes obsolete PODICIPEDIDJ*. Key to the Genera of the Family Podicipedidae1. A. Without a broad bifid, overhanging postorbital process. GROUP a. (Type P. cristatus.) With a wide and distinct temporal fossa. and strongly marked cerebral prominence; postorbital region of the frontal marked by a deep scar, for the temporalis muscle, the superior border of which has a rough edge; upper jaw longer than cranium. I do not feel justified in attempting to form " Keys" to the species, either for the skull or any other part of the skeleton, of the forms comprising the two sub-families dealt with in this paper. Inasmuch as of the Colyinbidae I have only two species, C.glctcialis and C. septentrionalis, and these are easily recognizable by the difference in size alone. In the Podicipedidae I have only 8 out of a possible 19 species of the genus Podicipes ; only one skeleton of Mchmoplwrus and no bones whatever of Podi/limbus. From what I can gather from our material, the difference between the three genera recognized in the British Museum Catalogue vol. xxvi. is very slight, and that between the species comprising these genera is even less. The genus Podicipes seems to divide itself into two groups-one of the type of P. fluuiatilis, and one of the type of P. cristatus. The differences upon which such separation rests concern the skull only and depend mainly upon size; the smaller species havine a relatively shorter and wider skull, and ill-defined temporal fossai |
