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EXPLANATION OF THE PLATES.

PLATE II.

Contains two figures; the first represents the different parts that compose the sternum, in the fossil animal, and their connection with the neighbouring bones; the second the corresponding bones in the ornithorhynchus paradoxus, to show their resemblance.

Fig. 1. The sternum, and bones connected with it, in the animal whose bones are found in a fossil state.

aa Two flat bones peculiar to the sternum of this animal and the ornithorhynchus.

b A flat bone behind which is concealed the union of the edges of the two flat bones just mentioned.

cc Two processes from this bone, by means of which it is united to the scapulæ.

dd The two scapulæ, which, united to the flat bones, form the glenoidal cavities of the shoulder joints.

eee A slender curved bone crossing the upper end of the sternum, and uniting the two scapulæ together.

ff The two first bones of the pectoral fin or paddle.

Fig. 2. The sternum and scapulæ in the ornithorhynchus paradoxus.

aa Two flat bones nearly similar to those in Fig. 1. united to the scapulæ, but making no part of the glenoidal cavity of the joint of the shoulder.

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b The bone corresponding to that marked b, Fig. 1.

cc Two processes similar to those in Fig. 1.

dd The two scapula which differ from those in Fig. 1. by extending below the two flat bones, and forming the whole of the glenoidal cavity of the shoulder.

ghij Four bones belonging to the sternum.

All the parts are of the natural size.

PLATE III.

The representation of a fossil bone of the natural size, which appears to belong to the same animal. Its place in the skeleton cannot at present be ascertained, since it is not yet known whether in this animal there is a regular pelvis. It bears a greater resemblance to the first bone of the paddle than to any other; so that if the animal has a posterior paddle, this must belong to it.