Zoological Affiuitien uf Aphanapteryx. 267 



is always to be recognized by the little interval which separates 

 the trochlea of the middle from that of the inner toe. It may 

 be remarked, however, that this interval increases as the birds 

 are better adapted for walking and running. Thus the inter- 

 digital slope is broader in the Rails than in the Coots ; it dis- 

 appears more in the genus Ti'ibonyx, and especially in Ocydromus. 

 Following step by step its modifications, we pass insensibly from 

 the normal form, which is presented to us in the tarso-metatarsus 

 of the Rails, to a form which at first sight would appear to be 

 altogether different, and is, so to speak, much more of a walker. 

 The fossil we are examining furnishes us, in some respects, with 

 an exaggeration of it ; for it is evidently better adapted for ter- 

 restrial locomotion than that of Ocydromus, and even offers 

 some resemblance to that of Apteryx. In Ocydrojnus the an- 

 terior metatarsal furrow is deeper than in our fossil ; the ten- 

 don of the common extensor of the toes passes under a bony 

 bridge ; the heel is hollowed inside by two pretty deep tendinal 

 grooves : but the general plan is the same; and it may be con- 

 ceived that if the modifications which we have just followed act 

 always in the same sense, they lead to the form which we find 

 in the bone found in Mauritius. There is, still, an enor- 

 mous difi'erence between the fossil and the tarso-metatarsus of 

 Apteryx; but it can, however, be considered to be a transition 

 between this last and the normal RallidcE', for what are the 

 anatomical modifications which this bone presents in Apteryx ? 

 The shaft of the bone is seen to be much shortened and widened ; 

 the intermuscular lines are efi^aced ; the digital trochleae, hardly 

 disposed according to the same plan, and separated by very 

 broad slopes, are stout and rounded. The heel is but slightly 

 prominent, and shows no tubular canal; it is hollowed by two 

 wide furrows, between which is a somewhat projecting ridge. 

 These peculiarities are of the kind which are offered by our 

 fossil compared with the tarso-metatarsus of Ocydromus, or this 

 last compared with its homologue in the Rails or the Water-hens. 

 The examination of the osteological characters leads us to think 

 that the bird from which the fossil in question came presented 

 undeniable analogies with the Rails. 



In the same deposit with this lower mandible and this turso- 



