362 ON THE GEXEKA XENICUS AND ACANTHISITTA. 



Johannes Muller of the syrinx of many of the Neotropical Mesomyodi *, 

 with those of G-arrod of Pitta t, or my own of Eurylcemus, Cijmbirhynchus^ 

 and Philepitta . In fact it resembles rather that of Todus, as lately descri- 

 bed and figured by myself ||. Externally the non-oscinine nature of Xenicus 

 and Acanihisitta is at once proclaimed by the structure of their wings, which 

 have a " first "If (tenth) primary nearly as long as the preceding one, 

 and by the non-bilaminate tarsus. The latter is covered almost completely 

 by a single large scute, with only some very obsolete traces of transverse 

 division below, whilst behind its edges are contiguous for the greater 

 length of the tarsus, leaving only small areas at each end of that bone, 

 which are covered by very small scutella of irregular form. The digits 

 are slender and compressed, the foot being slightly syndactyle by the 

 union of the fourth toe to the third for the greater part of its two most 

 basal joints. The tail is short and weak ; and there are only ten 

 rectrices in each of my specimens. As there is no evidence of a pair 

 P. Z. S. 1882, more having been present, this number of tail-feathers must be considered 

 to be that normal in the present family, twelve being that universal, with 

 a few isolated exceptions, in all other Passeres. 



In all other points, Xenicus and Acanthisitta conform to the general 

 Passerine type. There is no trace of a plantar vinculum. The tensor 

 patagii brevis has the peculiar arrangement characterizing the Passeres, 

 only slightly masked by the muscular fibres somewhat concealing the 

 two superimposed tendons, as is frequently the case in the short-and- 

 rounded-winged forms of the group. The glutens primus is well-developed. 

 The tongue is lanceolate and horny, with its apex somewhat frayed out 

 and its base spiny. The main artery of the leg is the sciatic. The 

 sternum has a single pair of posterior notches and a bifid manubrium. 

 In the skull the nostrils are holorhinal, the vomer broad and deeply 

 emarginate anteriorly, the maxillo-palatines slender and recurved. 



As regards the affinities of the Xenicidfe, the " haploophone " form of 

 their syrinx, combined with the complete loss of a vinculum, shows that 

 it is only with the PipridaB (including the Cotingidse), Tyrannidse, 

 Pittidae, and Philepittidae that they can be compared. From all of these 

 they differ markedly, however, in the number of rectrices, the ocreate 

 tarsus, and the nature of the syrinx, the latter never having the form of 

 a complete bony box, and never lacking a bronchial " intrinsic " muscle 

 in any of the families just enumerated. The Pittidse they approach 

 somewhat in their general fades, short tail, and long tarsus, though the 

 tarsal scutellation is different in the two forms. 



* Vocal Organs of Passeres : Oarrod's ed., Oxford, 1878. 

 t Coll. Papers, pi. xxvi. 



| Antea, pp. 140, 141, 142. Antea, p. 146. j| Antea, p. 347. 



^[ Sundevall is in error in assigning to these birds only nine remiges (Tentainen, 

 p. 47). 



