INTRODUCTION. vil 
work, and to accompany all the species, as distinguished by me, with a diagnosis, 
not only on account of the numerous additions made since the publication of 
Mr. Boulenger’s Catalogues of Batrachia, but also because the views of Herpetologists 
differ only too frequently as to the taxonomic value of characters used by them for 
specific distinction. In this latter part I have received valuable assistance from the 
authorities of the United States National Museum, Dr. Franz Werner of Vienna, 
Professor Béttger of Frankfurt, Professor Camerano and Count Peracca of Turin, 
Dr. A. Dugés, Professor Mobius, and M. Mocquard, either by the loan of or 
information concerning typical specimens: assistance for which I beg to return my 
best thanks *, 
The geographical limits fixed by the Editors for the scope of the ‘ Biologia’ are, in 
the North, the Rio Grande del Norte and the political boundary of Sonora and 
Chihuahua, and, in the South, the Isthmus of Darien. Lower California is excluded. 
The general features of the Reptilian and Amphibian Faunas of this area have been 
satisfactorily ascertainedf. Forming the connecting link between the two Neogzan 
regions, Central America possesses a Reptilian and Batrachian Fauna with the various 
constituent elements so mixed that, if only certain families or genera were taken into 
consideration, almost every district of this area could be associated with either the 
North- or South-American region. The tropical Fauna, of course, gradually changes 
into, or is replaced by, that of the temperate region, as we proceed from lower to higher 
latitudes ; but this change is not uniform throughout the breadth of the land; the two 
faunas overlap each other in deep and manifold indentations. ‘Tropical types are found 
to preponderate in the low lands of the Atlantic side, which expand into the broad 
Yucatan peninsula, and on the humid slopes of moderate elevation ; some extend to, 
and even reach northwards of, the Rio Grande. On the Western side they are found 
in similar localities, but in a narrower belt, along the Pacific coast. On the other hand, 
numerous types of the southern North-American Fauna are spread over Northern — 
* Unfortunately I have not had an opportunity of examining any of the specimens of Reptiles named by 
Cope. An application which I made to the authorities of the U. S. National Museum, at the commencement 
of the work, could not be acceded to at the time, as the materials were in Mr. Cope’s hands and had not been 
returned by him. 
+ Cfr. Cope, “ Zoological Position of Texas,” Bull. U.S. Nat. Mus. no. 17 (1880) ; Boulenger, Catalogue of 
Batrachia Gradientia, 1882, p. 104; Ann. & Mag. Nat. Hist. 1885, xvi. p. 77 (Lacertilia) ; Giinther, Eneycl. 
Brit. ed. ix. art. Reptiles (1885); Cope, Amer. Nat. 1896, pp. 886, 993; von Martens, Naturwiss. 
Wochenschrift, vol. i. (1901). 
