THE CYPRINODONTS. 67 



with a large blackish spot on the basal half, and a narrow edging of dark on 

 the outer border. Caudal of some tipped with darker. Males with six to 

 twelve narrow vertical bars of brownish on the flanks. 



Males 32 mm. ; females 43 mm. (Steindachner.) 



The details given in the description are insufficient for a very satisfactory 

 determination of the affinities or position of this species. The modification 

 of the anal, however, with its short intromittent organ would place it in 

 Poecilia rather than in Girardinus. 



XIPHOPHORUS. 



XiphophoTus Heck., 1852, Sb. Ak. Wien, I (1848), 291 ; Blk., 1860, Cypr., 482, — 1863, Atl., Ill, 140; 

 Kn. & St., 1865, Abh. Ak. Wien, 1864, X, est. p. 24 ; Jor. & G., 1S82, B. 16 U. S. Mus., 346. 

 Mollienesia Gthr., 1880, Intr., 617 (part). 



Body more elongate than that of Mollienisia, resembling the more slen- 

 der forms of Poecilia, compressed, with a moderately deep caudal portion. 

 Head depressed, crown slightly arched. Snout short, broad, subtruncate; 

 chin short, steep. Mouth wide, directed upward ; lower jaws longer, loosely 

 joined ; upper short, protractile. Dentition as in Molhenisia ; an outer 

 series of slender oar-shaped, hooked, movable teeth, behind which is a band 

 of smaller pointed ones. Dorsal larger than the anal and originating farther 

 forward. Anal opposed to the dorsal on males, with a short intromittent 

 organ. Ventrals small. Caudal deep, convex on the female, with the lower 

 lobe prolonged in a sword-shaped organ on the male. Scales large. Intes- 

 tine elongate. Type X. Hellerii of Heckel. 



Mexico ; Central America. 



The elongation of the body, and the modified lower lobe of the caudal fin 

 of the male, with the peculiar subvertebral processes of this sex, are the 

 characters on which is based the separation of this genus from Mollienisia 

 and Poecilia. In the species M. petenemis the caudal undergc:.^ a similar 

 change, though much less pronounced. On X. Hellerii the dorsal and ven- 

 trals are modified in the same manner as on Mollienisia, but not to the same 

 extent. The differences are hardly sufficient for genei'ic distinction, and, 

 perhaps, a more consistent disposal of Mollienisia and Xiphophorus might 

 place them as subgenera under Poecilia. 



