( -'61 ) 



OSTEOLOGY OF PALAEOLIMNAS CHATIIAMENSIS Forkes. 



In the large collection of fossil bird-remains from the Chatham Islands at the 

 Tring Museum bones of a large coot are very numerous. The credit of first drawing 

 attention to this extinct form is due to Dr. H. O. Forbes,* by whom it was regarded 

 as indistinguishable from Fidica newtoni of Mauritius. The same author also 

 recorded t the presence in these deposits of a second larger form, to which he gave the 

 name Fulica chathameiisis. Subsequently he pointed out a number of cranial 

 characters distinguishing these fossils from recent species of Fulica, and he therefore 

 established a new genus, Palaeolitnnas,\ for their reception. Jlilne-Edwards, in the 

 memoir above mentioned, accepts this generic separation of the Chatham Island coots, 

 but considers that there is only one species, the differences in size being merely due 

 to individual variation, a conclusion fully confirmed by examination of the very large 

 series of specimens at Tring. The same author has also pointed out a number of 

 characters by which the Chatham Island bird is distinguished from F. neuionl, and 

 Forbes' second name, Palaeolimnas chathamensis, is therefore adopted. § 



Although many portions of the skeleton of this bird have already been figured 

 and described by Milne-Edwards, it does not seem necessary for that reason to omit 

 all account of such an interesting form from the present paper, especially since the 

 opportunity of examining a nearly perfect individual skeleton will enable me to 

 supplement the previous description to a considerable extent. 



The skull (PI. IX., figs. 4, 5, 6). — The skull of Palaeolimnas is on the whole 

 extremely similar to that of recent species of Fulica, the chief differences pointed 

 out by Forbes and ]Milne-Edwards being — (1) the great antero-posterior curvature 

 of its upper surface; (2) the large size of the supraorbital impressions; (3) the 

 inflation of the frontal region. Ajiavt from tliese main differences, there are, how- 

 ever, a number of less obvious ones, some of which may now he referred to. In 

 Palaeolimnas the occipital surface is considerably wider, and, owing to the greater 

 development of the lambdoidal ridge, is better defined than in Fulica atra or 

 F. crlstata. iloreover the paroccipital processes are larger, and there is a well-marked 

 supra-foraminal ridge ; on the other hand, the occipital crest is less developed than 

 in the recent forms, and the foramen 'magnum is wider in proportion to its height. 

 Looking at the skull from above (fig. 4), it will be seen that the convexities in the 

 parietal region caused by the cerebral hemispheres are considerably less prominent 

 than in Fidica atra; but the most remarkable feature is the bevelling away of the 

 orbital margins, apparently caused by the large size of the supraorbital glands. As 

 Milne-Edwards has stated, the two impressions meet in the median lino between the 

 orbits like the sides of a roof. In many instances the actual crest of the ridge has 

 a narrow groove running along it and extending to the anterior end of the frontals ; 

 this is apparently the remnant of the frontal suture. Although this arrangement 

 seems to be the usual one, there is a very considerable range of variation in the 

 degree of development of the glandular impressions, and if (be extremes of the series 

 only were known, the different types of skull might well be referred to distinct 



* .\ature. Vol. XLVI. (1S92), p. 252. 



t Lac. clt. 



i Ibis (IS93), 1). 5J4. 



§ Kemains oE a large extinct coot, nearly equal in size to the present species, have been discovered 

 by Hamilton in a fissure in tlie limestone at Castle Rucks, Soutlilanil, New Zealand. This species (fulica 

 prisca Hamilton) is probably identical witli, or very similar to the present Torm. 



