Among the Plesiosaurian remains recently mounted for exhibition in the Reptile Gallery at the Natural History Museum is a very fine pelvic-girdle belonging to a species of the genus Cryptoclidus (Seeley), and forming part of the same skeleton (Leeds Coll., R. 2616) as the pectoral-girdle recently described and figured by the present writer. These specimens are perhaps the most perfect known, the bones being quite uncrushed, free from matrix, and, except that they are cracked and broken to a slight degree, in much the same condition as if they had been obtained by maceration from a recent reptile. They clearly belonged to an old individual in which ossification had nearly reached its maximum: this is shown (1) by the complete union of the coracoid and scapula with one another in the middle line closing the coraco-scapular foramen; (2) by the sharpness of some of the edges of the bones, e.g. of part of the anterior border of the pubis; (3) by the great solidity of the bones, and by the accuracy with which the pectoral and pelvic elements fit together to form the glenoid and acetabular cavities respectively, showing that the cartilage which separates them in the young animal had been ossified.