AND OTHEE EXTINCT BIEDS OF MATJEITIUS, 289 



size excludes at once the possibility of their being referable to any of the species 

 hitherto known, as the following measurements will show. We distinguish it, on 

 account of its small size, as Plotus nanus. 



Plotus nanus. P. arihinga. P. melanogaster, P. nov.-Twlland. 



mm. mm.- mm. mm. 



Left humerus 89 112 132 120 



Left tibia 61 77 86 78-95 



Distance from acetabular axis to ante- 

 rior end of sacrum 30 35 



Instance between ventral inner margins 



of the acetabuJa 14-5 15 



5. PoDicEPES, sp. inc. 



The proof of the former existence of Grebes in the Mare aux Songes rests upon one 

 single bone only, the right ulna ; but the latter agrees in all the essential points with 

 the corresponding bone of the genus Podicepes, notably the configuration of the 

 proximal and the distal articulations, and the existence of a sharply marked groove at 

 the upper outer distal condyle for the passage of the tendons of the extensor muscles, 

 and differs in all these characters from the corresponding bones of any other birds 

 which might otherwise possibly be taken into consideration, that doubts are excluded. 

 The total length of this ulna is 82 mm. It is consequently far too long and strong 

 for P. pelzelni, P. minor, or P. pJiilippensis. On the other hand, it is much too 

 short for P. cristatus and by 10 mm. shorter than that of P. ruficollis. It is, 

 however, slightly longer than the ulna of either P. cornutus or P. auritus, so that it 

 probably belonged to an insular form of one of these last-named species. 



6. BuTOKiDES MAUEITIANUS, sp. nov. (Plate XXXIV. figs. 6-8.) 



It is surprising that of all the Ardeine bones, referable to at least twelve individuals 

 of five different species, none belong to Ardea [Butorides) nigricollis, the only species 

 of Heron at present existing in Mauritius, while a pair of ulnae, one radius, four 

 metatarsi, and one coracoid must be considered as belonging to a species of short- 

 footed Heron hitherto unknown. The bones in question are all considerably shorter 

 than the corresponding bones of A. {Nycticorax) megacephala. The metatarsi agree 

 otherwise in every detail with those of the latter species ; this relative stoutness 

 indicates that they belonged to a Night-Heron or Bittern like A. megacephala. The 

 two ulnae cannot, unfortunately, be compared with those of A. megacephala ; their 

 length, 110 mm., compared with the length of the humerus of A. megacephala, 

 119 mm., shows, however, likewise that they were those of a considerably smaller 

 bird. 



VOL. xiii. — PART VII. No. 2. — August, 1893. 2 u 



