Xxli INTRODUCTION. 
The Cyprinide may be divided into four sub-families, viz. Cyprinine, Catostomine, 
Cobitidine, and Homalopterine, the first having a range nearly co-extensive with that 
of the family, the second being North American (with 2 or 3 species in Eastern Asia), 
the third occurring in Eurasia and Abyssinia, the fourth in Southern Asia. 
The Cyprinine, in addition to having the widest range, are by far the most diversified 
and the most numerous in genera and species, and may perhaps be regarded as the 
most generalized, especially as in some of the genera primitive characters are present 
(pharyngeal teeth in more than one series, lips normal, gill-membranes free from the 
isthmus, suborbitals broad) which are not to be found in the other sub-families. 
In the Cyprinine the maxillaries are entirely or in great part excluded by the pre- 
maxillaries from the upper border of the mouth. The Catostomine differ from them 
in that the margin of the upper jaw is formed in the middle by the small premaxillaries 
and at the sides by the maxillaries; these bones are hidden in thick fleshy lips, and the 
reduction of the preemaxillaries is, in my opinion, probably due to this fact. 
The Cyprinide may have originated in some part of the Indian region *, which is at 
the present day the richest in genera and species and where the most generalized forms 
occur. Boulenger, regarding the Catostomine as the most generalized group, considers 
that the Cyprinide may have originated in North America as an offshoot of the South- 
and Central-American Characinide. He explains the fact that in America they have 
not extended further south than Guatemala as due to competition with herbivorous 
Characinids; but as the most northern representative of the latter group (Curimatus 
magdalene) does not extend further north than Panama, this explanation is scarcely 
satisfactory, especially as Cyprinids and herbivorous Characinide are by no means 
mutually exclusive in Africa. 
The Catostomine comprise about seventy species belonging to about ten genera from 
North and Central America and three species belonging to about two genera from 
Eastern Asia. 
Ictiobus, with the dorsal fin elongate, includes about twelve species, in rivers east of 
the Rocky Mountains and the Sierra Madre, from the Great Lakes to the Rio Usuma- 
cinta in Guatemala. The Mexican species are four in number and are found in the 
southern tributaries of the Rio Grande and the rivers of Tamaulipas. J. meridionalis 
from the Usumacinta is the only member of the sub-family in the Neotropical Region. 
Cycleptus, with a single species ranging from the Mississippi to Tamaulipas, and a 
genus with two species in China are allied to Jctiobus. 
* The present distribution of the Cyprinids leads to the supposition that they originated in Indo-China at 
or before the beginning of the Eocene. 
