Order RALLIFORMES.l 



[Family RALLIDJE. 



NESOLIMNAS DIEFFENBACHI 



(DIEFFENBACH'S EAIL.) 



Cabalus dieffenbachii, Gray ; Buller, Birds of New Zealand, vol. ii., p. 121. 



Confined to the Chatham Islands and long since extinct. The only known specimen is in 

 the British Museum.* 



In his paper ' On the Extinct Birds of the Chatham Islands ' (Nov. Zool., vol. hi., p. 73) 

 Dr. C. N. Andrews says: "Milne-Edwards has shown that Aphanapteryx is likewise an Ocydromine 

 Bail which has undergone a similar series of modifications, and its similarity to Diaphora- 

 pteryx is so remarkably great that Forbes was justified in his hesitation in according the 

 Chatham Island bird generic rank ; but the inferences he draws from the simililarity of the two 

 forms do not appear well founded. He considers that their occurrence in Mauritius and the 

 Chatham Islands is strong evidence that these were formerly connected with the great Antarctic 

 Continent, for the existence of which a large body of evidence has been brought forward by 

 various writers. It is true that the geological structure of the Chatham Islands tends to show 

 that they form part of a continental area, since they are largely formed of sedimentary deposits 

 consisting of clay-slates, limestones, and various fossiliferous tertiary deposits, which, according to 

 Hutton, probably range from the Upper Eocene to the Upper Miocene ; but, on the other hand, 

 there is nothing in their present fauna to show that since their last emergence they have been 

 connected with any land area whatever. On the contrary, it seems clear that since that period 

 they have never been united even with New Zealand, for not a trace of any of the Dinornithidce , 

 Apteryx, Cnemiomis, Aptomis, or any of the flightless birds characteristic of those islands, have 

 been found in them. Moreover, as Mr. Forbes himself has pointed out, no fragment of the skele- 

 tons of Diaphorapteryx is recorded from New Zealand. This complete difference in the flightless 

 birds of the two areas does not seem to be outweighed by the occurrence of Hatteria. . . . 

 Dr. Gadow has, I think, given the true explanation of the likeness of Diaphorapteryx and Aphan- 

 apteryx to one another, namely, that it is the result of parallelism of evolution, or in other words, 

 similar conditions acting on similar organisms have produced like results. The ancestors in the 

 two cases, generalised Bails capable of flight, were probably of different genera, or, at least, species. 

 In the case of Biapliorapteryx this ancestor was most likely some widely spread form, such as 

 Hypotcznidiaphilippensis is at the present day, individuals of which from time to time reached New 

 Zealand, Lord Howe Island, and the Chatham Islands, the channels between which may formerly 

 have been narrower than at present. The modified descendants of these birds are now referred to 

 the genera Diaphorapteryx, Cabalus, and Ocydr omits, the most highly modified forms being the 

 outcome of earlier — the less altered, of later — colonisations. In any case, there can be but little 

 doubt that these Bails became flightless in the islands they now inhabit, and cannot therefore be 

 regarded as evidence of the former extension of land ; in other words, they are of no value in deter- 

 mining former geographical conditions, since they are themselves the outcome of the present one." 



* Another Ocydromine form, of much larger size, once inhabited the Chatham Islands, the fossil remains of which 

 were first discovered by Dr. A. O. Forbes, with the assistance of a local collector, Mr. Hawkins, after whom he named 

 it Diaphorapteryx hawkinsi. 



