ERRATA. PAGE LINE 4, 2, from bottom, _for_ procælian _read_ procœlian. 7, 13, _for_ Ossements _read_ Ossemens. 8, last line, paragraph (2), _for_ outermost _read_ innermost. 10, 21, } 11, 5, } _for_ Sömmering _read_ Sömmerring. 11, 13, } 14, note, _for_ Beyerischen _read_ Bayerischen. 15, 5, _for_ ?zygapophyses _read_ spinous-processes. 17, 6, from bottom, _for_ Herman _read_ Hermann. 37, 5, from bottom, _after_ "spine as" _insert_ "are" 92, line above 'the Dentary Bone,' _for_ Pterodactyle _read_ Pterodactyles. 97, 11, _for_ Günter _read_ Günther. 99, 4, _for_ Ichthyopteria _read_ Ichthyopterygia. 101, 11, from bottom, _for_ procælous _read_ procœlous. 102, 15, _for_ procælous _read_ procœlous. 111, 8, _for_ Sömmering _read_ Sömmerring. _For_ epipubic bone _read_ prepubic bone, pp. 61, 102, 109, 110, 111, and pl. 8. INTRODUCTION TO THE OSTEOLOGY OF THE ORNITHOSAURIA FROM THE CAMBRIDGE UPPER GREENSAND. -------------- Materials. The Cambridge Upper Greensand has yielded to collectors bones which illustrate nearly every part of the skeleton of the animals that are commonly named Pterodactyles. Large collections have been acquired for the Woodwardian Museum. A series of more than 500 bones have been arranged to exemplify the osteology and organization of the Ornithosauria in the area when the Cambridge Greensand was deposited. And this memoir is written to explain briefly some of the structures of the soft and hard parts of those animals which are exhibited or demonstrated by these relics. Another collection of nearly 400 bones has been arranged, which displays in association, as they were found entombed in the old Greensand sea-bed, the remains of the skeletons of thirty-three animals of the Pterodactyle kind. The whole of the remains from this formation hitherto gathered cannot be computed to have pertained to fewer than 150 individuals, which indicate a new sub-class of animals, two new genera and at least twenty-five new species.