214 THE VARIATION OF THE SCAPULA IN THE BATRACHIA. 



the pars acromialis and pars glenoidalis are separated from each 

 other by a cleft, or at least a notch (Bombinator and Pseudis). 

 This character seems to be of much greater importance than 

 mere size, and corroborates the conclusion of Wolsterstorff, who 

 says*: " Palceobatrachus verbindet im Systeme die Aglossa mit 

 den Arcifira/' 



In spite of generic stability the variation is enormous, par- 

 ticularly in the length of the shaft. Xenopus, on the one hand, 

 in which the scapula is absent or represented by the pars 

 glenoidalis only, ranging to Phyllo medusa, Ceratophrys, and 

 Heleioporus, in which it is enormously developed, in Heleioporus 

 being twice and a half the length of the prajcoracoid. 



It is astonishing that such a useful bone as the scapula should 

 have been overlooked for so long. The following key is based on 

 this character alone : — 



A. Proximal end of scapula entire '.. Pipid^;. 



B. Proximal end of scapula cleft. 



I. Length of scapula \ or less than \ length of praecoracoid. Discoglossidjj:. 

 II. Length of scapula more than \ length of preecoracoid. 



a. A large oval foramen pierced vertically in glenoid 



cavity ; pars glenoidalis greatly reduced Hylid.e. 



h. Foramen, if pierced vertically in glenoid cavity, 

 moderate or small ; often represented by a cleft 

 pierced obliquely or horizontally Pelobatid^;. 



BuFONIDiE. 



Ctstignatiiidjj. 



I am unable to find reliable family characteristics which 

 differentiate between the Pelobatidae, the Bufonidse, and the 

 Oystignathidae. 



* Op. cit. 



