108 ON THE STRUCTURES AND DISTRIBUTION OF THE 



This family was characterized by Dr. J. E. Gray, in Pruc. Zoological Soc. London, 

 1858, 142. 

 VIII. Prefrontals and pterygoids present. 



Parietals not embracing the broad frontals. 



Orbitosphenoid 



No dcntigerous plates on the parasphenoid bone. 



A postfronto-squamosal arch, sometimes liga'mentous. , 



Carpus and tarsus osseous. 



Vertebra3 opisthocoelian. 



Occipital condyles sessile. 



Pleurodelid^. — Genera Hemisalamandra, Neurergus, Lissotriton, Lophinus, 

 Euproctus, Cynops, Notophthalmus, Pleurodeles, Glossolega, Siranota. Regio Palce- 

 arctica ; three species in North America. 



These genera form a series measured by the increasing strength and ossification of 

 the post-frontoparietal arch, which has be'en pointed out by Gray and figured by Ger- 

 vais, Dumeril, and Duges. It is first bony in Lophinus : in Glossolega it is very 

 stout, and leaves but a small crotaphite foramen, while in Siranota it fills up the 

 foramen, being entirely continuous with the parietal bone. On this ground Dr. 

 Gray has regarded this genus as representing a family,—" Siranotidte," — but it does 

 not appear to be more different from Glossolega than the latter is from Neurergus 

 and Hemisalamandra.* 



The study of the Mammalia, the Rapacious, Pullastrine, Gallinaceous and Passe- 

 rine Birds, of the Sauria, Tortoises, Tailless Batrachiansf and Malacopterygian 

 Fishes, leads to the conclusion that these portions of the Fauna Neotropica represent 

 much lower stages in their respective series than do the same types in the Regio 

 Pala3otropica. In a few types, as Zygodactyl Birds and Ophidia, there is, as far as 

 our present knowledge extends, a seeming equivalency ; but in no single group can a 

 superiority be proven for the Fauna Neotropica ; the tests of the grade being ever 

 the retention of the characters of the incomplete stages of the extremes of the series, 

 the relations of generalized and specialized structure, or, where we have not yet demon- 

 strated thoroughly, by the afiinities with forms whose relations in these respects are 

 known. These relations coincide in hind with those contrasting the Faunas of earlier 

 and later geological periods, but not in degree, since they refer to the suhordinate or 



* The genera adopted are those arranged by me, Proc. Acad. 1862, 343. The preparations on which the 

 preceding investigations have been made are the collections of Prof. Baird and myself; the former in the 

 Museum of the Smithsonian Institution, Washington. 



t This is in opposition to the following proposition of Gunther, (Proc Zool. Soc. Lond., 1858,) the contrary 

 of which; I think, has been abundantly proven. He says : " Such a difference between the animal life of the 

 New World and that of the Old as pertains to other parts of the animal kingdom, is not to be observed in the 

 Batrachians. Dissimilarity and similarity of the Batrachia Fauna depeud upon the zones." 



