FISHES FROM THE RIVERS OF MEXICO. 
117 
The following new genera are described in this paper: Istlarius ; Xystrosus ; 
Falcula ; Xenendum. 
The following is a list of the new species* described: 
Istlarius balsanus. 
Notropis rasconis. 
calientis. 
Xystrosus popoclie. 
Falcula ohapalse. 
Characodon encaustus. 
Xenendum caliente. 
Xenendum xaliscone. 
Pcecilia limantouri. 
Xipliopliorus moutezum®. 
Eslopsarum arge. 
Cliirostoma ohapalse. 
promelas. 
diazi. 
Cliirostoma crystallinum. 
lermse. 
ocotlane. 
Ciclilasoma steindachneri. 
Heros istlanus. 
Neetroplus carpintis. 
MEASUREMENTS. 
The measurements given in the tables of this paper were made by means of a pro- 
portional scale. It is believed that they will show, in an approximately definite way, 
some of the variations of certain characters useful in determining the relationships of 
the species. They are expressed in hundredths of the length of the body, which is 
measured from the tip of the snout to the end of the last vertebra. The depth of the 
body is measured at its deepest part; depth of caudal peduncle at its narrowest 
place; length of caudal peduncle from base of last anal ray to end of last vertebra; 
length of head from tip of snout to posterior edge of opercle; length of snout from its 
tip to anterior margin of orbit; length of caudal fin from end of last vertebra to tip 
of upper caudal lobe. Only fully-developed fin rays are counted. The rudimentary 
rays of dorsal and anal, when closely adnate to the first branched ray, are counted 
with it as 1 ray. When the last ray is double and the two parts connected at the base, 
it is counted as 1 ray. Scales in the lateral series are counted to base of caudal fin; 
transverse series from insertion of ventrals or anal, whichever is nearer middle of body, 
upward and forward ; on caudal peduncle, upward and forward at narrowest part. 
LIST OF SPECIES. 
LEPISOSTEIBiE. 
1. Lepisosteus osseus (Linmeus). 
Plentiful in Tampico markets ; said to be taken in the river and neighboring lagoons. 
2. Lepisosteus tristcechus (Bloch & Schneider). 
Collected in the markets of Tampico. 
SXLURID2E. 
3. Ameiurus dugesi Bean. 
Obtained in the markets of Guadalajara and in the Laguna de Chapala, Jalisco, Mexico. 
We classify this sjiecies with the genus Ameiurus, believing that Villarius [ Villarius Rutter, Proc. 
Cal. Acad. Sci., ser. 2, vol. 6, 1896, 256 (pricei)] is an invalid genus. Villarius was supposed to be distin- 
guished by the presence of scattered villi on the skin of the sides. Such villi are, however, common 
to many cat-fishes, notably, A. nebulosus, A. catus, Noturus flavus, Ictalurus punctatns, Leplops olivaris, 
and Istlarius balsanus. Small specimens of Ameiurus dugesi have the caudal fins tipped with black. 
4. Ictalurus furcatus (Le Sueur). 
One specimen purchased in Tampico market, said to have been caught in the Rio Tamesoe. 
"These species appear at almost the same date in the fourth part of Jordan & Evermann’s 
“Fishes of North and Middle America.” 
