200 MISS JOAN B. PROCTER ON THE VARIATION 



his specimen it is evidently incorporated in the prsecoracoid, as 

 described above. 



X. calcaratus Buchh. & Ptrs. — Scapula as in X. Icevis, but 

 more easily distinguished, as the glenoid cavity extends to the 

 upper border. 



X. clivii Peracca. — Scapula with a distinct, but vestigial, 

 triangular shaft, the apex of which narrowly separates the head 

 of the prsecoracoid from the supra-scapula ; pars glenoidalis as in 

 X. Icevis ; pars acromialis absent. 



Example. 



Length of prsecoracoid 10 units. 



,, scapula (at base) 3 - 3 ,, 



n (upper edge) -55 „ 



,, ,, shaft 1'7 ,, 



Breadth of ,, (expanded end) 2 - 8 ,, 



Length of supra-scapula 9 - 4 ,, 



In the tadpoles and young of X. Icevis, X. calcaratus, and 

 X. muelleri the reduced condition of the scapula is somewhat 

 less marked than in the adults ; an extremely short shaft is 

 present, precisely as in the adult of X. clivii. If ontogeny may 

 be taken as a guide to phylogeny, X. clivii should be considered 

 the most primitive species in the genus. 



This vestigial form of scapula, which even in X. clivii does not 

 exceed two-fifths of the prsecoracoid in length, and which may 

 be completely suppressed in other species, renders Xenopus 

 unique both among the Aglossa and Arcifera. 



Hymenochirus Blgr. 



H. boettegeri Tornier. — Scapula much reduced, but less so than 

 in Xenopus. Distal end expanded, proximal end narrowed, 

 entire ; the whole wedge-shaped. Proximal end strongly over- 

 lapped on outer surface by head of prsecoracoid. No glenoid 

 cavity. 



Example. 



Length of prsecoracoid 10 units. 



,, scapula (greatest) 5"5 ,, 



„ „ (upper edge) 3-1 „ 



Breadth of ,, (expanded end) 3"3 ,, 



„ (least) 2-2 „ 



Length of supra-scapula 8*9 ,, 



Pipa Lau'r. 



P. americana Laur. — Scapula compact, very much reduced, 

 almost triangular when seen from within. Shaft vestigial; pars 

 acromialis strongly overlapped by head of preecoracoid on inner 

 surface ; a strong crest and protuberance on outer surface, bor- 

 dering the glenoid cavity ; pars glenoidalis much depresssed when 

 seen from without, not distinct from pars acromialis when seen 

 from within, 



