Carinate Birds from Central Madagascar. 349 



The various grooves and muscle-attachments are rather better 

 marked iu tlie fossil than in the living form ; this seems to 

 be the case also in Chenalopex jnf(jil. This specimen is 

 24 mm. iu length. Compared with the radius of Phoeni- 

 copterus, which in length it resembles, it is found to be much 

 stouter and to differ in many other respects. 



The proximal three-fourths of a right ulna wanting the 

 olecranon process, and part of a left, correspond in size with 

 the above-mentioned radius. They also agree closely in 

 structure with the same bone in Sarcidiornis and Chenalopex, 

 though, as might be expected, in the larger bird the muscle- 

 impressions, particularly the insertion of the bracldalis 

 anticus, are more strongly marked. The largest diameter 

 of the middle of the shaft is 10 mm. 



Perhaps the most characteristic bone of this bird is the 

 metacarpus (PL VIII. fig. 7), but unfortunately only the 

 proximal half of that from the left side is preserved, and 

 even from this the free portion of the third metacarpal is 

 broken away. Its most striking character is the presence 

 of a very long spur-like process formed by the production 

 downward and forward of the fused first metacarpal. The 

 terminal half of this process has an irregular roughened 

 surface which indicates that it was not invested with a claw- 

 like spur such as occurs in Chauna and some Plovers, but 

 was most probably covered by rough hardened epidermis, 

 like the similar processes in Chenalopex and Sarcidiornis. 

 The I'csemblance of this bone to the metacarpus of Chena- 

 lopex pugil is remarkable, the only differences perceptible 

 being that in this bird the spur is rather stouter and more 

 curved forward ; the size is nearly the same. The spui' 

 on the wing of Plectropterus is borne on a process of the 

 radial carpal, and is therefore not comparable with that of 

 Chenalopex and Centrornis. 



The dimensions of the imperfect metacarpal are : — 



Greatest width of upper end 31 mm. 



Length of spur measured from tip to 

 middle point of articular surface for 

 first phalangeal of digit I . 26 



Width of metacarpal II 9 



