XXXII. CHIROSTOMA 75 



Body gracefully slender, the contours gradually converging back- 

 ward and forward from the middle and deepest point of the fish's 

 length; greatest depth, 5.2 (4.7 to 5.4)^^ in length without caudal; 

 depth of caudal peduncle, 2.6 (2.2 to 2.6) in its length behind end of 

 anal base, 2.6 (2.5 to 2.8) in length of head to opercular margin 

 (excluding membrane). Head, 4.2 (4.0 to 4.35). Orbit placed an- 

 teriorly, its hinder margin being equidistant from tip of snout and 

 from margin of branchiostegal membrane; length of orbit, 4.2 (4.0 to 

 4.4) in head; length of moderately blunt snout, 3.4 (3.4 to 3.6) ; least 

 interorbital width, 3.6 (3.4 to 3.8). Upper jaw strongly curved, but 

 less oblique posteriorly than in chapal^ or jordani ; maxillary extend- 

 ing backward almost (or quite) to the vertical from the anterior margin 

 of the orbit; length of upper jaw, 2.8 (2.6 to 3.0) in head; mandible 

 strong, elevated within the mouth, its lower margin slightly convex 

 to its blunt tip, which projects a little farther forward than the pre- 

 maxillaries ; lips rather thick posteriorly. Teeth fine, disposed in bands 

 along jaws ; teeth of outer mandibular series slightly enlarged ; teeth 

 a little enlarged in an inner and an outer series on the premaxillary, 

 between which there is a band of fine teeth, narrowest anteriorly ; outer 

 premaxilliary teeth visible from above in some specimens ; vomer with 

 a few teeth (not evident in some specimens). Gill-rakers, 4 -)- 15 (in 

 a paratype) as in humboldtianum, much fewer and stouter than in 

 CHAPAL^, the longest scarcely more than half as long as the orbit. 



Air bladder extended backward nearly to above middle of anal 

 base. Vertebrae 42 (in a paratype), fewer than in bartoni. Now 

 BARTONi, by reason of its large and entire marginal scales, has been 

 placed in a subgenus or genus supposedly distinguished from Chirostoma, 

 to which REGANi is referable, by its fezver vertebrae. It is such facts 

 as this that have led us to unite all of the CHiROSTOMA-like fishes into 

 a single undivided group. 



Scales moderate, reduced in size on the nape; in 45 (43 to 49) 

 series from above branchial aperture to end of last vertebra; in 12 

 (11 to 14) series above anal origin; in 7 (6 to 8) series between origins 

 of dorsals. Scale margins finely crenate. 



Fin formula: dorsal, IV (or V)-I, 10 (9 to 11); anal, I, 18 

 (15 to 20) ; pectoral, 14 (12 to 14). First dorsal inserted a little before 

 vertical from tips of ventrals (which do not quite reach to anus), equi- 

 distant from base of caudal and from middle of snout ; first dorsal when 

 depressed extending backward about three-fourths the distance from its 

 origin to the second dorsal ; its length thus measured contained 2.35 



25 Measurements in parentheses are those of ten paratypes from Xochimiico, 

 75 to 94 mm. long to caudal. 



