Art. XXIII.—On a New Genus of Rallidæ.
Pl. XX., figs. 1 and 2.
[Read before the Wellington Philosophical Society, 1st September, 1873.]
In a paper read to this Society last year I described a new species of Rail, from the Chatham Islands, under the name of Rallus? modestus (Trans. N.Z. Inst., V., p. 223), at the same time expressing an opinion that it would form the type of a new genus. Since then the skeleton of the other specimen obtained by Mr. H. Travers has been prepared by the late Dr. Knox, and an inspection of this skeleton has so confirmed my previous opinion that I now no longer hesitate to place it in a new genus, of which the following is a diagnosis:—
Cabalus, gen. nov.
Bill longer than the head, moderately slender and slightly curved, compressed in the middle and slightly expanding towards the tip; nostrils placed in a membranous groove which extends beyond the middle of the bill, openings exposed, oval, near the middle of the groove. Wings very short, rounded; quills soft, the outer webs as soft as the inner, fourth and fifth the longest, first nearly as long as the second; a short compressed claw at the end of the thumb. Tail very short and soft, hidden by the coverts. Tarsi moderate, shorter than the middle toe, flattened in front, and covered with transverse scales; toes long and slender, inner nearly as long as the outer; hind toe short, very slender, and placed on the inner side of the tarsus; claws short, compressed, blunt.
The bird is incapable of flight, and the stomach of the specimen dissected by Dr. Knox contained only the legs and elytra of beetles.
The skeleton is so very remarkable that I feel compelled to make a few
observations on it, but without attempting any description, for doing which I have not the requisite anatomical knowledge.
The sternum (of which a front and side view, twice natural size, are given on Plate XX., figs. 1, 2) is very small and quadrangular in shape, the breadth being about .6 of the length, but constricted below the costal border; the anterior end is deeply concave between the articular grooves for the coracoids, which are widely separated, and this concavity is smooth without any prominences or median process. The only other birds that have this remarkable concave outline of the anterior end of the sternum are, as far as I know, Apteryx, Aptornis, Didus, and as Dr. Hector informs me, Notornis—all, it will be noticed, except Apteryx being extinct forms. The costal border of the sternum only forms one fifth of the lateral border, and has articulations for four sternal ribs only. The lateral processes are long and slender, commencing not far below the costal border, and in a line with the apex of the keel; they are not dilated at the ends. The keel is so much reduced as to be almost obsolete, as also is the furculum. The scapula makes a right angle with the coracoid. The pelvis is somewhat similar in shape to that of Rallus pectoralis, but the ilia are not expanded anteriorly, and the pelvic disc is broader in proportion behind, increasing in breadth regularly from the antacetabular portion of the ilium. The posterior outlets of the neural canal are much reduced, and the ilio-neural orifices quite obliterated. There are 9 dorsal and 12 cervical vertebræ.
The following are some of the more important dimensions:—
|Length of sternum to the coracoid groove||.7|
|Height of keel||.1|
|Length of femur||1.2|
Dr. Buller, in his Birds of New Zealand (p. 180), says that he has no hesitation in considering my Ralluss modestus as the young of Rallus dieffenbachii; but this is unquestionably a mistake. Both the birds obtained by Mr. H. Travers were full-grown, one accompanied by her young one, and the other containing well-developed ova; they were both exactly alike in colour and dimensions, in neither of which do they show any approach to the colour and dimensions of R. dieffenbachii, as may be seen by comparing descriptions of the two; while in all known Rails the young soon acquire a plumage approaching in colour to that of the adult, and always attain their adult plumage before breeding. In its body, tail, wings, legs and feet,
C. modestus is a smaller bird than R. dieffenbachii, while the bills of the two are of nearly the same length; but in all Rails the legs and feet attain the full size very early, and long before the bill acquires its full length. R. dieffenbachii is also closely related in colour and form to R. pectoralis, while the skeleton of C. modestus differs largely from that of R. pectoralis. It is needless to pursue the subject further, but I must say that it is much to be regretted that the skin of C. modestus, which is one of the most curious of New Zealand birds, should have been sent to Dr. Buller, in England, on purpose that it might be figured, and that it has been returned to New Zealand with the remark that it is the young of a bird already figured in his book, and without its having been submitted to Dr. Finsch, who, as Dr. Buller is aware, is engaged on a book on the birds of New Zealand.