In Birds the rudimentary thumb (or second finger, according to Owen) has no connection with the carpus. In the Penguin, _Aptenodytes Patagonica_, it has disappeared altogether, and there then remain two fingers of which the outer one (seen from the front as we have placed our animal) is the larger, and has the greatest number of phalanges, precisely as in Ornithosaurians. Moreover the wing-metacarpal, in the Penguin especially, is seen to unite with the carpus directly under the radius, as is the case with the Cambridge Ornithosaurians. Hence it follows that in Pterodactyles the thumb is not developed, and that the wing-finger is not the little finger, but the index finger, precisely as in Birds. If Goldfuss gave a reverse arrangement it was because the hand in his specimen, as is proved by the claws, was upside down. In the immature state the distal carpal of Pterodactyle appears to have been composite. Notwithstanding the opinions of eminent German philosophers to the contrary no reptile has a carpus comparable to that of the Pterodactyle. If some of them have two rows of bones and a pisiform bone, so have mammals, and the mammalian arrangement is not more like the Ornithosauria than is that in Reptiles. METACARPAL BONE. Pl. 6. Case. Comp. Tablet. Specimen. =J= _b_ 5 1-3 The illustrations of this bone comprise 31 specimens. Nos. 1 to 15 are examples of the proximal end, and Nos. 16 to 31 show the distal trochlear end of the bone. No. 1, which is nearly entire, gives the form and proportions of the wing-metacarpal in one species, but a knowledge of its variableness in German forms would guard against an assumption that all the other Greensand species were to be restored on the plan of this example. It is 3-5/8 inches long, to which three-eighths of an inch may be added for the distal articulation, making the length up to 4 inches. The proximal end is not well preserved, but in its wide measurement is 5/8ths of an inch; the distal end in the same measurement is about 3/8ths of an inch. A large example from the Chalk, in the Museum of C. Moore Esq. of Bath, shows the bone more attenuated distally. No. 1 is compressed so as to be oblong in section at the proximal end, and ovate in the middle of the shaft, which is slightly smaller than the distal end. One of the lateral outlines is straight; the other is concave. The bone is straight. In No. 30 the shaft where thickest measures less than 1/4 of an inch, becoming nearly circular in section. The shaft of No. 31 measures nearly an inch in width at its distal end, rather more than half an inch in thickness. No. 10 is 1-1/2 inch wide at the proximal end and 7/8ths of an inch thick. No. 9 would not have measured less when perfect than 2-1/2 inches over the proximal end, so that if it had the proportions of No. 1 it would have measured when entire not less than 16 inches in length. The Proximal End.