ORDER RHYNCHOCEPHALIA. II33 



genus Mesosaurus, and the ischia being almost identical with those 

 of the Amphibia. The tarsus also resembles that of Mesosaurus in 

 having five distinct bones in the distal row ; while the humerus (as 

 in the latter) has an entepicondylar, or ulnar, foramen. 



That PalcRohatteria is a primitive type connecting the later Rhyn- 

 chocephalia with the Amphibia there can be no reasonable doubt ; 

 and although it presents many points of affinity with Mesosaurus, 

 these resemblances are those which we should expect to find in all 

 transitional types, and do not necessarily imply that all the forms in 

 which they occur should be placed in the same group. 



Suborder i. Sivledosauria. — This group is represented by the 

 genus Champsosaurus, typically from the Lower Eocene of North 

 America, which may be regarded as a somewhat specialised Rhyn- 

 chocephalian, showing a remarkable affinity, in the general structure 

 of its skull and vertebral column, to Hyperodapedon. Dr Baur ob- 

 serves that this genus agrees with the other Rhynchocephalia in the 

 loose condition of the otic bones, and in the nature of the costal 

 articulations ; and since it has a fixed quadrate, two temporal ar- 

 cades, and abdominal ribs, there appears no good reason for its 

 ordinal separation. The adaptation to an aquatic life has, however, 

 necessarily produced considerable structural modifications of secon- 

 dary import. The correctness of these observations has been re- 

 markably shown by the researches of M. Dollo, who finds that the 

 structure of the palate, and the position of the posterior nares, and 

 the general arrangement of the teeth, closely accords with that 

 obtaining in Hyperodapedo?i. The suborder may be characterised 

 as follows : The facial portion of the skull is produced into a long 

 rostrum ; the splenial bone enters into the mandibular symphysis ; 

 the tail and pelvic limbs are elongated ; the vertebrae are amphi- 

 ccelous ; and the ribs have no uncinate processes. 



Family Champsosaurid.e. — In the type and only known family 

 the nares are single and subterminal ; the maxillary and anterior 

 mandibular teeth are large and not fixed to the bone ; there is a 

 series of smaller teeth on the palatines and vomers, separated by a 

 groove from those of the maxilla ; while there is also an irregular 

 mass of small teeth on the pterygoids, which are completely united 

 in the middle line ; the posterior nares form very narrow slits on 

 the sides of the palate ; and there is no parietal foramen. There 

 are some twenty-five presacral vertebrae, and the neuro-central suture 

 is persistent. Remains referred to C/zampsosaurus have been found 

 not only in the Lower Eocene of North America, but also in the 

 corresponding horizon of Belgium and Rheims ; the latter specimens 

 having been described under the name of Simadosaurus. One of 

 the specimens from Rheims indicates an animal of about nine feet 

 in length, but other examples appear to have been of considerably 



