XXI. ARCHOMENIDIA 55 



and H. B. Baker July 23, 1910. This material fixes the hitherto imper- 

 fectly known habitat of this species as the east coast streams of central 

 Mexico, and makes possible a supplementary description of the species 

 (based upon seven specimens 41 to 55 mm. long to caudal). 



Body rather slender and moderately compressed, resembling that of 

 Menidia m. menidia in lateral aspect, except that the anterodorsal con- 

 tour is more nearly horizontal ; belly broadly rounded anteroventrally ; 

 greatest depth contained 4.9 to 5.3 times in total length to caudal ; least 

 depth of caudal peduncle, 2.8 to 3.0 times in length of head (including 

 the opercular membrane). Length of head contained from 4.0 to 4.3 

 times in the length to caudal ; head a little less than half as broad as 

 long, and not quite so broad as deep. Length of orbit a little greater 

 than the width of the slightly convex interorbital, notably greater than 

 length of snout, slightly greater than postorbital length of head, and 

 contained 2.6 to 2.7 times in head. Premaxillary widely dilated posteri- 

 orly; the strongly oblique maxillary extended backward not quite to 

 below the anterior orbital margin; the tip of the lower jaw included; 

 the gape very strongly arched, the physiognomy approaching that of 

 Cynolebias (Pceciliid.e). Teeth of the outer of the two rows in both 

 jaws decidedly stronger and more regularly arranged than those of the 

 inner series ; the outer premaxillary teeth exposed, and visible from 

 above when the mouth is closed, they being directed outward as well as 

 downward ; those toward the front of the premaxillaries becoming strong- 

 ly curved canines. 



Anus advanced in position, as in no other known species of the sub- 

 family, located about midway between the insertion of the ventral fin 

 and the origin of the anal, nearer tip of snout than caudal base. Ventral 

 insertion equidistant from anal fin and from head ; origin of the anal a 

 little more distant from the tip of the snout than from the end of the 

 middle caudal rays ; origin of the first dorsal over, slightly before, or 

 slightly behind the anal origin ; distance between the origins of the two 

 dorsals considerably less than twice the length of the first dorsal when 

 depressed, longer than the base of the second dorsal, and about as long 

 as head behind middle of eye ; second dorsal beginning over middle of 

 anal base, higher than long, falcate like the anal; anterior and highest 

 anal rays as high as the body; length of anal base a little greater than 

 length of head ; the ventrals when folded together concealing the anus, 

 but not reaching the anal. Fin rays ; dorsal, IV or V — I, 9 or I, 10 ; anal, 

 I, 18 to I, 20. 



Scales in 40 to 42 series from branchial aperture to end of hypural. 

 in 10 series (8 main rows) above anal origin ; in 7 series between origins 

 of dorsal fins. Scale margins evenly rounded or broadly and shallow- 



