The large proportional size of the neck-vertebræ is common to some birds, and is conspicuous in many mammals, like the Llama. In most mammals where the vertebræ have a cup-and-ball articulation, the ball is in front, as it is in the dorsal vertebræ of the penguin, so that those vertebræ are not comparable with Pterodactyles, although on the under side of the centrum they similarly give off a mesial process below the cup, and a lateral process below the ball on each side. The neural spine in Pterodactyle is commonly more developed than is the case with long-necked birds or mammals. Reptiles such as Crocodiles and Lizards have the neural spines of the neck-vertebræ well developed. Birds differ from Pterodactyles in the peculiar articulation of their vertebræ. In both the centrum is often depressed, in both it is concave from side to side in front, and convex from side to side behind, but in birds it is also convex from above downward in front, and concave from above downward behind, while the reverse arrangement obtains in Pterodactyles. A similar condition to that of the bird is seen in the neck-vertebræ of the Kangaroo, of Man, and several mammals, only the vertical curves are less marked. Vertebræ concave in front, and convex behind, and devoid of cervical ribs, are met with among the Lizards, but neither Monitor nor Iguana offer any parallel to the form of the cervical vertebræ of Pterodactyle, which is best matched among Marsupials and Birds. Birds commonly have more vertebræ in the neck than have Pterodactyles, which in that respect resemble mammals and some Lizards. Dorsal Vertebræ. Pl. 10. Case. Comp. Tablet. Specimen. =J= _c_ 3 1-20 Twenty specimens are mounted to exemplify pectoral and dorsal vertebræ. Like the cervical vertebræ, they include two types of form, one with the centrum flat, figured in pl. 2. fig. 20-22 of the memoir on Pterodactylus Sedgwicki, and regarded by Prof Owen as anterior dorsal; and the other form with a convex centrum, figured 24-25 of the same plate of the same memoir, regarded by Prof. Owen as posterior dorsal. Following the analogy of birds such determination is as well supported as the similar reference of the two types of cervical vertebræ to anterior and posterior parts of the neck, but fuller materials compel a reference of the two types of dorsal vertebræ to two different genera. Nos. 1, 3, 6, 7, 8, 9, 10, 14, 15, 19 belong to the flat type. Nos. 2, 4, 5, 11, 12, 16, 17, 18 exemplify the convex type. Dorsal vertebræ are rare fossils; and in the associated sets of bones never more than four dorsal vertebræ are found, rarely more than one. No specimen of the type with a convex centrum occurs in the associated sets.