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portion of a disk. In some genera, it is deeply emarginate, as in Lacertilia; 

 but it is usually entire, as in Sauropterygia. 



The humerus is a small bone, exceedingly wide in Clidastex and Plate- 

 carpus, and narrower in Liodon. It is wider distally than proximally, has a 

 flat shaft, and presents ho condyles, but elongate articular surfaces only. 

 The radius is also a wide bone, especially dilated at its distal and exterior 

 border. The ulna is much less expanded ; the extremities being subequal, 

 and the shaft contracted, but flat. The carpals are small, flat, and few in 

 number; they are subround or hexagonal in outline. The phalanges, meta- 

 carpals, and metatarsals are flattened near the carpus, but soon become less 

 expanded and more cylindric at the extremities and at the shaft. The term- 

 inal ones are flat. 



The pelvic elements are slender, and the inferior but loosely-united on 

 the middle line below. The ilium is the longest, and is quite attenuated 

 above, and without immediate contact with a vertebra. The pubis is clavate 

 and flat ; the wider portion next the ilium, and pierced with the foramen 

 observed in Lacertilia, The ischium, is broader, and has an angulate poste- 

 rior outline. The femur is equally or more slender than the humerus (see 

 the plate of Platecarpus crassartus), and, in Liodon, resembles it in form. It 

 is flat, without condyles, wider distally, and with a trochanteric tuberosity at 

 the proximal end. The fibula is a very wide bone, sometimes constituting 

 three-quarters of a disk. The tibia is, like the ulna, a more slender bone 

 than its companion, with contracted shaft, and subequally-expanded extrem- 

 ities. 



The phalanges much resemble those of marine turtles, and the pes and 

 manus are of a less robust type than in any other order of marine reptiles. 



Affinities. 



The significance of the ordinal characters has been already pointed out. 

 There remain a number of peculiarities, not certainly of ordinal value, which 

 are, nevertheless, necessary to consider in estimating the relations of these 

 reptiles to others : 



1. The form and position of the coronoid bone are those seen in eryci- 

 form serpents. 



2. The articulation of the splenial with the angular is only paralleled in 

 the pythonoid and allied serpents. 



