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Show 1889.] MR. W. K. PARKER ON STEATORNIS CARIPENSIS. 165 turnae," cannot be improved. W h y they should now stand midway between Swifts and Cuckoos must be determined by those who have the power of reading and interpreting the hard sentences of Nature. Bearing all these difficulties in mind, we may now look into the details of the supposed ancestral form of the Goatsucker type. II. The Skull. In a large, but evidently rather young, specimen the " rostrum," measured in a straight line, is 29 millim. long; the skull 37*5 millim. In the skull of a smaller, but older, specimen the measurements are, rostrum 27 millim., skull 35 millim. The bony rostrum (Plate XVII. fig. 1) in both cases is deflected 8 millim. below the general palatal plane ; this is seen to a much greater extent when the horny covering is on. Therefore, there is in this case, still more than in Corythaix, and other Cuculines with a decurved beak, a quasi-Raptorial appearance. Indeed, the skull of Steatornis is very much like that of the Ceylon Owl (Ketupa ceylonensis) ; a likeness which is intensified by a similar development of the " basi-pterygoids " in both cases. I believe that this is mere isomorphism. The measurements of the lesser skull are as follows:- millim. Length of rostrum 27 Length of skull, proper 35 Width of fronto-nasal hinge 11 Width of narrowest part of frontal region ' .... 12*5 Width across postorbitals 34 Width across occipital wings 31 Width across quadrato-jugal hinges 35 Thus we see that the length and the greatest breadth of the skull, proper, are equal. This at once stamps the skull with an Owl-like character, which is intensified by the narrowness of the upper interorbital tract, the large size of the very open orbits (19 millim. long, 16 millim. deep), and the form of the upper beak, or "rostrum." Put side by side with the skull of Ketupa ceylonensis, it seems as if it must belong to an allied genus, at least; but in the details of its structure it is soon found to be Cuculine. The skull of the Ceylon Owl and that of its Strigine congeners, like that of most Diurnal Rapacious birds, is indirectly Desmognathous. The skull of Steatornis, however, is doubly Desmognathous (Plate XVII. fig. 3 ), and has its alinasals (Plate XVII. figs. 1, 2, al.n.) ossified in the true Coccygomorphine fashion ; these parts remain cartilaginous in the Owls2. 1 In the lesser skull this part is a little wider than in the two large specimens, whilst the surface is gently concave in it, and convex in the larger specimens. Are these sexual differences ? 2 There is, I believe, but one point in Ornithology in which I a m out of touch with m y friend Prof. Alfred Newton. W h y he should doubt the near kinship of the Owls to the Harriers and Hawks I cannot imagine; see his remarks in the otherwise unassailable and excellent article " Ornithology." Encycl. Brit. 9th edit. vol. xviii. p. 471. PROC. ZOOL. Soc-1889, No. XII. 12 |
