ON THE GENERA XENICUS AND ACANTHISITTA. 361 



The genus Xenicus was founded by the late Mr. G. It. Gray * for the 

 reception of the Motadlla lonyipes of Gmelin t, Lafresnaye having some 

 twenty years previously established Acanthisitta for Span-man's Sitta 

 chloris +. 



Subsequent ornithological writers have pretty unanimously assigned 

 both these forms to the " Certhiidae " or their immediate neighbourhood, 

 in company with Sitta, Sittella^ and their allies. The peculiar structure 

 of the tarsus in Xenicus first induced me to examine these birds more 

 closely, with the unexpected result that I find that the two genera in 

 question are true Mesomyodian forms, and therefore in no intimate 

 degree related to such Oscines as those just mentioned. 



The subjoined drawings of the syrinx of Xenicus with which in all 

 points Acanthisitta appears to agree in every essential respect will 

 show that it has none of the complex nature of that organ in the Oscines, 

 the thin lateral tracheal muscle terminating on the upper edge of a 

 somewhat osseous box formed by the consolidation of the last few 

 tracheal rings, and there being no other intrinsic syringeal muscle !* Z. S. 1882, 

 whatsoever. The box has a well-developed an tero -posterior pessular p< 

 piece. The bronchial rings are throughout of quite simple form, and 

 are separated by but narrow intervals. None are modified in form to 

 serve for the insertion of a vocal muscle, as the latter terminates higher 

 up, as already described, on the tracheal box, and therefore quite out of 

 the region of the bronchi. 



The lateral position of the single syringeal muscle is that characteristic 

 of all the Mesomyodian Passeres, though in most of these it terminates 

 on one of the bronchial rings, and not, as in the birds under consideration, 

 oil the sides of the trachea. This may easily be seen by comparing the 



Syrinx of Xenicus longipes, much enlarged. 



A. From in front. B. From behind. 



m. Lateral tracheal muscle. 



accompanying figures of Xeniciis with the beautiful series given by 



* Ibis, 1862, p. 218. t Rev. Mag. Zool. 1842, Ois. pi. ixvi. 



Mus. Carls, fasc. 2, no. 33. 



