130 



We have additional species from — 



North Carolina (Mosasaurns) • - 1 



Mississippi (Platecarpus) - 1 



Nebraska (Mosasaurus) - 1 



Making, with the others from — 



New Jersey - - 15 



Alabama 7 



Kansas . . - 26 



A total of. : . . 51 



Of these, I am not acquainted with any species which extends its range 



into two of the areas above named; while some of these districts possess 



peculiar genera. It is, nevertheless, premature to draw any conclusions as to 



geographical range, as most of the species are known as yet from but few 



specimens. 



History. 



The knowledge of the structure of the animals of this order has been 

 due, almost exclusively, to the labors of three paleontologists, viz, Georges 

 Cuvier, Prof. 0. C. Marsh, and the writer. Cuvier determined the characters 

 of the dentition, and of the anterior regions of the skull, and of the vertebral 

 column. Professor Goldfuss added little to this beyond the description 

 of the parieto-quadrate and postorbito-malar arches. The writer ascertained 

 the structure of the posterior part of the skull, including the walls of the 

 brain-case, the'suspensorial apparatus, the pterygoid and palatine bones, and 

 the median hinge of the lower jaw; also, of the scapular arch and fore and 

 hind limbs, except the phalanges. On this basis, the determination of the 

 affinities of the order was made. Professor Marsh determined, for the first 

 time, the presence of hind limbs, and described the pelvic arch; he also 

 determined the relations of the phalanges of the lore limb, the presence 

 of two small supernumerary cranial bones, and the probable existence 

 of dermal scuta. 



CLIDASTKS. Cope. 



Vertebral column exceedingly elongate, I lie vertebras united by the 

 zygosphenal as well as the usual articulation ; the zygosphenc elevated but 



