582 Analijtical Notices of Books. 



species illustrated by Mr. Yarrell, had been already figured by 

 Dr. Parsons, in the Philosophical Transactions, but in that re- 

 presentation it was detached from the sternum. The figure now- 

 given shows it in its natural situation, which not only better ex- 

 hibits its true character, but also furnishes a point of comparison 

 with the nearly corresponding structure of the very rare Anthro-^ 

 poides Stanley anus ^ Vig., the representation of which succeeds. 

 The structure in the Anas atrata^ L., is shown to be intermediate 

 between that of the common, and that of the wild. Swan, the 

 trachea descending, but so far only as the central circular portion 

 of the furcula. In the Anas semipalmata^ Lath., the extremely 

 elongated trachea lies between the pectoral muscle and the skin, 

 and a striking variation was observed between the two specimens 

 examined by Mr. Yarrell. In the first of them it was situated 

 on the left side, extending along its whole length, and possessing 

 an extra convolution, the trachea elongating itself first along the 

 second series of the four parallel longitudinal tubes formed by 

 it, returning by the third, then curving successively downwards, 

 backwards, and upwards, to the first series, and returning along 

 the fourth : in this instance the left clavicle was shorter and 

 wider than the right. In the second specimen the right clavicle 

 was enlarged, and here the tubes were parallel without any extra 

 convolution ; the elongation of the trachea passing backwards 

 along the third series, returning by the second, passing backwards 

 again along the first, and returning by the fourth. Whether these 

 particular dispositions of the trachea are uniformly accompanied 

 by the deviations in the form of the clavicle which respectively 

 accompanied them in these instances, can only be ascertained by 

 repetitions of the dissections as often as opportunities occur. 

 The paper is concluded by an outline of an arrangement of the 

 British species of Ducks, founded upon internal as well as external 

 conformation, in which two divisions are pointed out, and the 

 species referrible to each are enumerated. As an abstract of Mr, 

 YarrelTs views on this subject will be found in our report of the 

 Proceedings of the Zoological Club, we refrain from entering 

 here into particulars respecting them. In illustration of this 

 part of the communication, we may however mention that figures 



