Another kind of pelvis is that in which the ilium extends a short way in front of the acetabulum, in which the pelvic bones inclose a much larger space. These include the Cambridge Ornithosaurians, the Rhamphorhynchus, and the Dimorphodon, and form another well-marked family. These long-tailed Pterodactyles subdivide into three sub-families--Rhamphorhynchæ, Dimorphodontæ, and Ornithocheiræ. The four families may then be defined thus: _Pterodactylæ_. Tail short. Hind-legs long. Ilium narrow, extending far anterior to the acetabulum; ischium extending behind the acetabulum. Epipubic bones ficiform. Head with the middle holes large, often confluent with the exterior nares. Jaws toothed to the anterior extremity. _Rhamphorhynchæ_. Tail long and stiff. Hind-legs short. Pubis and ischium small, oblique to ilium, which extends less far anteriorly than in Pterodactylæ. Epipubic bones narrow and bent; they unite mesially and form a three-sided bow in front of the pelvis. Head with the middle holes and nares both small. Jaws never toothed to the anterior extremity. _Dimorphodontæ_. Tail long and stiff. Hind-legs long. Pubis and ischium forming an expanded sheet of bone at right angles with the narrow ilium, which extends as far behind as in front [prepubic bones triangular (?) attached by the apex of the triangle]. Head with the nares and middle holes large. Quadrate bone large. Jaws with large teeth at the extremities, and small teeth behind. No sacrum. _Ornithocheiræ_. Tail long and flexible. Hind-legs short. Pelvis as in Dimorphodontæ. [Epipubic bones with a small attachment, form unknown.] Head with the quadrate bone small. Sacrum of not fewer than three vertebræ. In the Pterodactylæ the genera are-- _Pterodactylus_ (Cuvier), in which the exterior nares are at the sides of the face, very large, and only partially, if at all, separated by bone from the small middle hole of the head. The head is elongated. The neck is long. Among others, it includes the species P. longirostris, P. Kochi, P. scolopaciceps, P. longicollum. _Ornithocephalus_ (Sömmerring), in which the anterior nares are entirely separated from the middle holes of the head, both being small, and the latter exceedingly small. The head is short The neck is short. The large ischium appears to be excluded from the acetabulum, and the ilium appears to extend less far forward than in Pterodactylus[AA].