I therefore regard the Pterodactyles as forming a group of equal value with birds, for which group the name Ornithosauria is here used. It cannot form a separate class, because they have a fundamental organization in common; and it cannot form an order of birds, because its differences from birds are greater than those of an order. It is a group which itself probably includes several orders, and must constitute a sub-class, which finds its place in nature side by side with birds and between mammals and reptiles, thus:-- Mammalia. \ | | Ornithosauria. Aves | Reptilia. / Restoration. Of the form and size[W] of the animals from the Cambridge Greensand, an idea will best be given by a few measurements. [Footnote W: There are Ornithosaurians hereafter to be described compared with which the largest at present known will seem diminutive. A vertebra of one such, from the Wealden, is contained in the British Museum (numbered 28632). The centrum alone is between 9 and 10 inches long and 8 inches deep. It is named Streptospondylus, but constitutes a new group of Ornithosaurians. Nothing so gigantic exists in the Woodwardian Museum. Another vertebra of the same or an allied genus has been figured by Prof. Owen as the tympanic bone of ?Iguonodon (Fossil Reptilia of the Wealden, Part 2, pl. 10).] In the species Ornithocheirus nasutus (Seeley), =J=._c_.2.11.1: The premaxillary extends for 6 inches without reaching the nares. The lower jaw is 3/4 of an inch deep at the articulation. The four cervical vertebræ are each 1-1/2 inch long. The sternum measures 1-1/2 inch over the facets for the coracoids. The humerus is 2-1/16 inches over the proximal end, the radial crest not being preserved. The coracoid is 1-1/4 inch over the proximal end. The scapula is about 3-1/2 inches long. The proximal carpal (imperfect) is 1-5/8 inch wide. The distal carpal is 1-1/2 inch wide. The lateral carpal is 1-1/4 inch long. The wing-metacarpal is 1-1/4 inch wide at the proximal end, and 7/8 inch wide at the distal end. The proximal end of the first phalange is about 1-5/8 inch wide. The proximal end of the second phalange is less than an inch wide. The claw-phalange (imperfect) is about 1-1/4 inch long. The femur is 4 inches long. Putting the animal together, the bones give this size : Head 1 ft. 3 in. long. Neck 9 " (_Back and sacrum_) ? 8 " (_Tail_) ? 10 " With the hypothetical parts, this would give a length of about 3 ft. 6 in. from the tip of the snout to the tip of the tail. Then Humerus 8 in. long. (_Fore-arm_) ?1 ft. 0 " Carpus 2 " Metacarpus 10 "