294 PROCEEDIN'GS OF THE ACADEMY OP 



We may also compare such extended metamorphoses with those of cosm ica 

 matter, such as when, in the course of ages, a primaeval vapor has in a short 

 time collapsed to the liquid form, or as when the vast of liquid in turn has 

 shrunk to its solid condition; both alilie for ages approaching their change, 

 yet stationary in external relations till the moment of transition has arrived. 



The following are the zoological relations of the groups already compared : 



The most generalized group of fishes of the Regio Neotropica is that of 

 Characins. Its type, in respect to fin structure, which Js common to all the 

 Malacopterygians, is that of an undeveloped stage of the Acanthopterygians, 

 the adipose fin being an undeveloped cartilaginous fin and the cartilaginous 

 fin an undeveloped spinous fin.* It may be said to be the highest among 

 Malacopterygians if we look to the complete oviducts, opercula, jaws, etc., 

 , but it is the lowest as removed farthest from the extreme of Malacopterygian 

 peculiarities, as being most generalized or embracing representatives of all 

 the rest, and approaching nearest the types of the past — the Ganoids. For 

 example, Butyrinus and Vastres may be compared with Amia. The family is 

 distributed chiefly in the Southern Hemisphere. 



The genus Orestias, which Agassiz says is characterized by a feature which 

 exists in the immature state of all other Cyprinodonts, — the absence of ven- 

 tral fins, — is only found in the Neotropical region. 



Of the venomous serpents, the inferior group, the Proteroglypha, belong to 

 the Southern Hemisphere, and the Australian and Neotropical regions al- 

 most exclusively embrace by far the greater proportion. Australia con- 

 tains none other. 



The Iguanian lizards are lower than the Acrodont, exhibiting a larval type 

 of dentition, and one characteristic of all lower Sauria and Batrachia. The 

 only acrodont type of Ophiosaura (Trogonophis) is Old World. 



The New World Teidse have not the extent of ossified temporal roof that 

 their representatives, the Old World Lacertids have. So the chiefly Neo- 

 tropical Anguidffi have the tongue partly of papillose type of their Old World 

 representatives, the Zonuridae, and partly the smooth or scaly type of the 

 cosmopolite Scincidte, which are inferior to them. 



The snake-like forms of the families of the Lacertiiia Leptoglossa greatly 

 predominate in the Southern Hemisphere; also those with undeveloped pal- 

 pebrse. 



The Neotropical type of Testudinata is quite coincident with the family 

 Characinidas in relations. It is, like it, largely distributed over the Southern 

 Hemisphere, and like it may be regarded, in respect to its pelvic pecularities, 

 as higher than the remaining types, but in its generalized character and re- 

 lationship to the past periods may be called lower. 



The Neotropical type of Batrachia Anura, that is the Arcifera, is lower in 

 developmental characters than the opposed series, the Raniformia ; such of 

 the latter as are found in its limits partake in some way of larval incomplete- 

 ness. The Arcifera are c'hiefly distributed elsewhere in Australia, where 

 no Raniformia exist.f Those genera of Old World Raniformia of the lowest 

 or toothless group, which display the least development of the cranial bones, 

 as Bra-chymerus and Breviceps, are of the Southern Hemisphere. — South 

 African. 



The Pullastrine birds are a generalized group, inferior to the group op- 



* Kner Ueber den Bau der Flossen. 



t The Eucnimisbicolor Gray would appear to be an exception, were its generic and sub- 

 ordinate affinities truly represented by its name. I have examined the type specimen 

 through tlie kindness of Dr. Giinther, and can state that it is nor an Ixalus,(= Eucnemis), 

 and does not even belong to the Raniformia, but is an Areifer of the family Hylidse. If 

 it be not a young C:ilamita or Hyla, it will be a Hvlella near the H. ca rnea type. 



Gunthor'stMtes that Hylorana erythraea has been found at the extreme northern 

 noint— Cape York— of Australia. If so, the case is parallel to the occurrence of the Hani- 

 form Ranula in northern South America. 



[Oct. 



