GENERA OF THE ARCIFEROUS ANURA. Ill 



Miocene plants, and between American Cretaceous and European Eocene plants, are 

 of exactly contrary significance. Of the same meaning is the appearance of true 

 Crocodiles* in American Cretaceous, equal European Eocene. 



As progress is the rule in palaeontology, the lapse of time will probably see a later 

 equivalency of some kind between the characters of the products of the inferior 

 Zoological Regions, e. g., Australis, Neotropica, and of those characterizing the 

 highest, — e. g., Palaaotropica, at the creation of man, — and mostly still remaining. 



The ready and rapid naturalization of Pala3otropical and Paltearctic plants in the 

 North and South American and Australian regions, is a remarkable feature often 

 noticed.-]* This will furnish the future paleontologist with the explanation of the 

 modification of fiora of a region on the introduction of a new epoch, and that by no 

 course of descent within that region; and constituting a nearer equivalency, as 

 above proposed, with that higher iiora established long since in the Eegio Palseo- 

 tropica. 



The extent of time during which the regions owe their products to migrations and 

 modifications, may have been limited to periods or epochs only. In respect to 

 terrestrial cold-blooded vertebrata, the following facts in their geographical distribu- 

 tion are patent ; they have been observed also in other types :| 



First, the identity of many of the boreal genera throughout the earth; second, the 



* With regard to the amphiccelian Crocodile genus Hyposaurus Owan, of the New .Jersey Green Sand, I 

 would state that it differs in one feature from all known estioct Crocodiliaus. The neural spines of the cervi- 

 cal vertcbraa are acuminate, of considerable — finally, of great — height, the anterior standing transversely on 

 the neural arch, the median subtetragonal, the posterior, as usual, longitudinal in section. In an anterior 

 cervical vertebra, length 2 in., the spine is 2 in. 10 1. above the ceiling of the arch, and is acute ; it receives a 

 strong lateral wing from each posterior zygapophysis, which does not disappear till near the tip. These en- 

 close a deep groove on each side behind, with a strictly perpendicular posterior median rounded rib ; in front 

 a narrow keel extends from the tip to the neural canal ; the lateral alaj are curved backwards. On a more 

 posterior cervical, the lateral alaa are very heavy, short and rounded, and enclose no groove with the slightly 

 projecting posterior vertical rib, while the anterior keel has become a strong compressed wing, dividing two 

 shallow anterior grooves ; breadth and length equal in section. In a last cervical, length 2 in. 2 1., the longi- 

 tudinal section (equal about an inch) is longitudinal cuneiform, owing to the projection of the anterior ala. In 

 an anterior dorsal the section is longitudinal (1 in. 5 1.) ; the lateral ribs remain at the base only, and the 

 posterior carina is strong and sharp ; it is acuminate, and was probably subacute, but is broken at tip ; if re- 

 stored would measure 4 in. 6 1. at least. 



This creature possessed some kind of elevated dorsal carina, probably dermal, as in some Anolidce and 

 Iguanidae, though the spines are not acute and ribbed in the latter. Their appearance in Hyposaurus suggests 

 some kind of conic dermal horny sheath as defensive weapons ; the vertebral line could not in any case have 

 been covered by flat bony plates, as in ordinary Croeodilia. (See Leidy's Cretaceous Eeptiles of the United 

 States, 18Gf), p. 18.) 



t See Dr. J. D. Hooker's article (Linnajan Society) on Naturalization of European Plants in New Zealand, 

 and Prof. A. Gray's Botany of the Northern United States. 



X A. Murray on Coleoptera, Old Calabar. Trans. Linnaean Soc. Loud., 1863. 



