Systematic Position of Zeledonia coronata. 19 



Of the larger Thrushes, Geocichla seems undoubtedly one 

 to take a very low position. This is borne out partly by the 

 form of the tympanic cavity (PL II. fig. 2), which is inter- 

 mediate in character between that of Sialia and Turdus, and 

 partly by the presence of vestigial basipterygoicl processes. 

 The presence of the latter is somewhat remarkable (PI. II. 

 fig. 6). Unfortunately I have but one skull of the genus 

 Geocichla — G. monticola. But traces of these processes 

 probably occur in other species of this genus. Few other 

 Passerines retain any vestige of these buttresses. 



The Tympanic Cavity. — The study of the free edge of 

 the tympanic cavity reveals some curiously interesting facts. 

 The simplest condition, perhaps, which this region presents 

 among the Passeriformes is to be met with in Menura (PI. II. 

 fig. 5). Here the free edge of the lateral occipital wing 

 meets, at a sharp angle, a sinuous ridge running from the 

 squamosal head of the quadrate. To the inner edge of the 

 lip of this ridge the tympanic membrane is attached, and 

 stretching across becomes attached to the lateral occipital 

 wing very near its free edge, so that the tympanum lies very 

 close to the surface. 



This type appears in a large number of widely different 

 groups, and the fact may be regarded as an additional 

 indication of its primitive character. 



The Turdiformes appear to have departed from this type 

 along two different lines. 



The ground-type of both forms appears to be represented 

 in Sialia (PI. II. fig. 3). In this genus the line formed by 

 the lateral occipital wing, after meeting the ridge described in 

 Menura, which runs from the squamosal head of the quad- 

 rate, is continued upwards and forwards, then sharply 

 downwards on to the squamosal process in the form of a low 

 and barely perceptible ridge. 



In the Ruticillinse the free edge of the lateral occipital 

 wing is continued upwards and forwards in the form of a 

 strong ridge to the postorbital process, so that the ridge 

 forming the anterior border of the meatus in Menura now 

 becomes overhung by a sort of cave. This feature is still 



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