THE PLESIOSAURS 



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a shortening of the bones of the upper segments, and an increase in the number 

 of bones corresponding with those of the toes of ordinary reptiles. In the true 

 plesiosaurs (Plesiosaurus) of the Lias, the ribs of the neck were articulated to the 



FRONT AND SIDE VIEWS OF A NECK VERTEBRA OF A PI.ESIOSAURIAN. 

 pr.z. and pt.z. anterior and posterior articular surfaces of the arch; co. rib. 



vertebrae by two heads; whereas in the later cimoliosaurs (Cimoliosaurus} of 

 the Oolites and Chalk, such ribs, as shown in the figure of a neck vertebra, were 

 single headed. Some of these creatures were of huge size, attaining a length of 

 between thirty and forty feet; certain of the species from the Cretaceous strata 



UPPER ASPECT OF THE SKELETON OF THE LARIOSAUR, A SMALL PLESIOSAURIAN. 



having a neck much exceeding the body and tail in length, and containing as many 

 as forty vertebrae. Marine and carnivorous in their habits, these formidable 

 creatures probably lurked in shoal waters from whence they darted their long necks 



