CIMOLIOSAURUS RICHARDSONI. 175 



lived in the deep seas, visiting the land only occasionally. 

 It has a weak spinal column : the two faces of the centrum 

 nearly meet in the centre, and the neural arches are unanchy- 

 losed, in which respect it differs from Plesiosaurus. The humerus 

 and femur of some Plesiosauri e.g., Plesiosaurus Manselii have 

 a third bone in addition to the ulna and radius, and to the 

 tibia and fibula, which T. W. Hulke, Esq., F.R.S., names the 

 os intermedium, and places it between the ulna and radius, 

 tibia and fibula, the homologue of which is found in the front 

 and hind limbs of some living Saurians. A very interesting 

 morphological question arises as to the possibility of tracing the 

 homology of these bones and their relation to the carpal and tarsal 

 elements of the higher vertebrates. I have already referred to 

 this splendid Plesiosaurian specimen in my paper on 

 the fossil reptiles of Dorset, 'and expressed my opinion that it 

 might possibly turn out to be Plesiosaurus plicatus of Phillips. 

 I am now inclined to change my mind and to call it 

 Murceno,wints Leedsii Seeley, a subgenus of Plesiosaurus 

 characterised by its shoulder and pelvic girdles having 

 only one coraco-scapula and one obturator foramen, and by a 

 difference in the union of the neural arches, as well as by 

 distinct forms of the ulna and radius, tibia, and fibula. 

 Possibly these differences will not be held sufficient by Mr. Lydekker 

 to justify Professor Seeley's separation. This palaeon- 

 tologist is now engaged in tabulating and arranging the 

 fossil reptilian remains in the British Museum ; the 

 result of his labours on the Crocodilia and Deinosauria will 

 soon be before the public, as the volume is now in the printer's 

 hands, and Avill be doubtless as invaluable an addition to Palseon- 

 tological literature as are his five volumes upon the Fossil Mammalia 

 of our National Museum. The remains of this Plesiosaur were 

 found in a bed of Oxford clay in the neighbourhood of Weymouth 

 last winter, and through the indefatigable and intelligent industry 

 of Mr. and Mrs. Richardson, of " Montevideo," they have been 

 built up in their present satisfactory condition. The head is 



