192 MR. C. TATE REGAN ON THE 
‘The present paper deals mainly with the material in the British Museum, including 
the types of the species described by Giinther and Boulenger, but the author, during 
a visit to Paris, has been able to examine all the types of the species belonging to this 
family which have been described and figured by Castelnau and most of those of 
Cuvier and Valenciennes. In addition, some of the types of species described by 
Eigenmann have been received on loan, since the reading of this paper, from the 
Museum of Comparative Zoology, Cambridge, U.S.A., and descriptions of these are 
incorporated, ‘The author wishes to express his gratitude to Mr. Boulenger for his 
ever-ready advice and help ; to Prof. Vaillant, through whose kindness he was permitted 
to examine the specimens in the Jardin des Plantes; to Dr. Pellegrin for his great 
courtesy and personal attention during his visits to the Paris Museum; and to 
Dr. Garman, who has sent to the British Museum examples of several species 
previously unrepresented in its collection, and, in the case of those species which have 
been described from one or two specimens only, has lent the types. 
A tribute must be paid to Dr. Steindachner for the excellence and accuracy of his 
descriptions of so many fishes of this family, which have made it a comparatively easy 
matter to assign species described by him to their natural systematic position without 
having seen actual specimens of them, 
The paper of Prof. and Mrs. Eigenmann on the “ South American Nematognathi” 
has been of considerable assistance, especially proving of value as a ground-work and 
for purposes of reference. 
In the present paper 189 species are recognised as valid, 34 of which are described 
as new to science. Our knowledge of the geographical distribution of these 
species is so very incomplete that generalisations are of little value. Most of the 
genera seem to be represented in the principal river-systems of South America, 
the rivers south of the La Plata system excepted, and the species seem in many cases 
also to have a very wide distribution, as might be expected when it is considered that 
the Amazon system actually communicates with that of the Orinoco on the north, 
whilst the head-waters of the southern tributaries of the Amazon are in many cases 
only separated by a few miles from those of the rivers of the La Plata system. Whilst 
it is clear that the Magdalena, Orinoco, Amazon, and La Plata systems, and also the 
coast-rivers of Eastern Brazil, have each several characteristic species which do not 
extend into other river-systems, still in the present state of our knowledge it is 
difficult to say which are the species with their distribution thus restricted. 
Two important genera, Chetostomus and Arges, occur only in the Andes of Peru, 
Ecuador, Colombia, and Venezuela, and are characteristic of mountain-streams in 
which the other genera of this family are not found; both have been recorded from 
considerable altitudes, and it would almost seem that each newly explored valley may 
be expected to furnish some new form. 
