Carinate Birds from Central Madagascar. 315 



coverer. Examination of the distal extremity of the tibio- 

 tarsus (PL VIII. figs. 1 & 2) shows at once that we are 

 dealing with an Anserine bird ; the very deep channel for the 

 extensor tendons, spanned by a transverse bridge which stands 

 in the middle line, together with the form of the articular 

 condyles_, are all perfectly characteristic of the group. There 

 are, however, a number of notable peculiarities. The most 

 striking of these are the extreme length and slenderness of 

 the shaft and the relative shortness of the fibular crest. 

 In its general proportions the tibia of Chenopis, particularly 

 of the extinct New Zealand species C. sumnerensis, Forbes, 

 seems to approach our fossil most nearly ; on the other hand, 

 there are some important differences, e.g. in Chenopis the 

 fibular crest is much longer, and in other parts of tlie 

 skeleton the two birds are very dissimilar. 



The distal end resembles that of the tibia of Cygnus in the 

 width of its articulation, but diff'ers from it and approximates 

 to the type characteristic of the more terrestrial Geese in the 

 very slight degree to which it is bent inward. Comparison 

 of the tibia with those of a number of Geese shows that, while 

 diff"eringfrom tliem in the great length and relative slenderness 

 of the shaft, it in many respects approaches those of Chena- 

 lopex, Plectropterus, and Sarcidiornis. The similarity to the 

 tibia of the first named is very great, both in the form of the 

 articular condyles and of the tibial bridge, but the distal 

 extremity is somewhat more inflexed and its articulation 

 wider than in Chenalopex pugil. The tibia of Sarcidiornis 

 differs from our fossil in the greater depth and narrowness 

 of its intercondylar groove. Cereopsis is also different, the 

 characters indicating a terrestrial mode of life being in that 

 genus more highly developed than in any other Anserine 

 bird. 



The dimensions (in millimetres) of the tibia are given 

 on p. 346, those of the tibiae of some other species being 

 appended for comparison. 



In size, proportions^ and general structure the femur 

 (PI. YIII. fig. 3) is almost identical with that of Plectroptei'us, 

 being mucli less massive and having a more clearly-defined 



SER. VII. — VOL. III. .V li 



