NORTH AMERICA AND THEIR VERTEBRATE FAUNA. lOQ 



Limnoscelis. — While a true Cotylosaur, and similar to Diadectes in many 

 points of its structure, Limnoscelis was probably much more aquatic in habit. 

 The weak tarsus and carpus, largely cartilaginous, could not have supported 

 the body of the animal in the posture of a terrestrial creature. The flatter 

 head, with the orbits nearer to the upper surface, and the longer and more 

 powerful tail, are all aquatic characters. 



It would seem that we have in these two animals, very similar in a geheral 

 way, adaptations, on the one hand, to terrestrial life, the animal feeding per- 

 haps on littoral molluscs, and, on the other hand, to an aquatic life, the animal 

 seeking its active prey in the water, and spending much of its time there. 



The families Labidosauridce and Captorhinidce contain the smaller Cotylo- 

 saurus, which unite the general characters of the order with those of a greater 

 agility and a more active life. The firm carpus and tarsus of the Labido- 

 sauridce, a terrestrial character, is combined with a broad, fiat head, such as 

 is usually associated with aquatic forms. It is probable that the animal lived 

 near the shore, almost equally at home on the land or in the water. The 

 captorhinids were probably of similar habits, but, as mentioned in the dis- 

 cussion of the teeth, were fitted for a diet of hard-shelled creatures. 



Table showing Terrestrial and Aquatic Adaptations and Food Habits. 



Amphibia: 



1. Aquatic, powerful swimmers, active, raptorial: 



Cricotus, Chenoprosopus. 



2 . Aquatic, perhaps burrowing in the mud : 



Lysorophus, Gymnarthrus, Cardiocephalus (?). 



3. Semiaquatic; probably fair swimmers, slow moving, raptorial, lurking for prey; 



Eryops, Trimerorhachis, Trematops, Acheloma, Zatrachys, Parioxys (?), Aniso- 

 dexis (?), Tersomius (?). 



4. More largely terrestrial, slow moving: 



Cacops, Aspidephorous, Dissorhophus, Alegeinosaurus. 

 Reptilia: 



1 . Semiaquatic, swift moving, raptorial : 



Poliosaurus, Varanosaurus, Varanoops, Theropleura, Pcecilospondylus, Ophiacodon. 



2. Semiaquatic, slow moving, lurking for prey, carnivorous: 



Limnoscelis. 



3. Terrestrial, active, raptorial: 



Clepsydrops, Dimetrodon, Bathygnathvis , Sphenacodon. 



4. Terrestrial, slow moving, carnivorous or insectivorous: 



Seymouria, Labidosaurus (Littoral). 



5. Terrestrial, slow moving, moUuscivorous, perhaps partly herbivorous: 



Diadectes, Chilonyx, Bolbodon, Bolosaurus (?), Captorhinus, Desmatodon, Dia- 

 sparactus, Pantylus. 



6. Terrestrial or arboreal, very active, insectivorous: 



Areoscel^s. 



7. Terrestrial, active, at least partly moUuscivorous: 



Edaphosaurus. 



8. Terrestrial, active, phytophagous (^(ie Williston) , moUuscivorous: 



Casea. 



THE ASSUMPTION OF ARMOR AND ITS MEANING. 



When, in the development of a fauna, a stage is reached where certain 

 forms begin to assume armor, it is evident that the individuals of that fauna 

 have reached a very perfect adjustment in their stu-roundings. Certain 



