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 
Peecilia rather than in Girardinus. 
XIPHOPHORUS. 
Xiphophorus Heck., 1852, Sb. Ak. Wien, I (1848), 291; Blk., 1860, Cypr., 482, — 1863, Atl. ITI, 140; 
Kn. & St., 1865, Abh. Ak. Wien, 1864, X, ext. p. 24; Jor. & G., 1882, 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 Peecilia, 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 Mollienisia; 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. /ellerii 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 subyertebral processes of this sex, are the 
characters on which is based the separation of this genus from Mollienisia 
and Precilia, In the species M. pefenensis the caudal undergoes a similar 
change, though much less pronounced. On X. Zellerii 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 generic distinction, and, 
perhaps, a more consistent disposal of Mollienisia and Xiphophorus might 
place them as subgenera under Poecilia 
