16. p(EciLiA. 343 



is contained four timea and one-fifth in the total length (without 

 caudal) in females, and thrice and one-fourth in males, the males 

 having the body much higher and shorter. The length of the head 

 is one-fifth of the same length in the female, and one-fourth in the 

 male. The diameter of the eye equals the length of the snout, is 

 two-sevenths of that of the head, and somewhat more than one-half 

 of the interorbital space. The origin of the dorsal fin is further 

 distant from the root of the caudal than from the occiput, and cor- 

 responds to the eleventh or twelfth scale of the lateral line. Origin 

 of the anal opposite to the fourth ray of the dorsal (in the female). 

 Dorsal fin of moderate size, anal rather small, but pointed ; caudal 

 scaly in its basal third. The free portion of the tail is compressed, 

 rather high, its least depth being one-half of its length, and equal 

 to the length of the head, without snout. There are seven longi- 

 tudinal series of scales on each side of the tail. Lateral line rather 

 indistinct. Greenish, each scale with a black vertical spot. Dorsal 

 and basal half of the anal irregularly and finely marbled with brown. 



The male has the dorsal fin somewhat elevated, the longest ray 

 being rather longer than the head. Anal fin modified into an in- 

 tromittent organ, and advanced to between the ventrals, in front of 

 the dorsal. Tail strongly compressed, and much higher than in the 

 female, its least depth being equal to the length of the head. 



Lake Peten. 



a-6. Male (5 inches long) ana females (6 inches long). From Mr. 



Salvin's Collection. 

 c-d. Males, 4 inches long. From Mr. Salvin's Collection. 

 e. Female, 5 inches long : skeleton. From Mr. Salvin's Collection. 



8. Poecilia sphenops. 

 Pcecilia sphenops, Cuv. 8f Val. xviii. p. 130, pi. 526. 

 D. 9. A. 8. L. lat. 28. L. transv. 8. 



The height of the body is contained thrice and a third in the total 

 length (without caudal), the length of the head thrice and two-thirds ; 

 the diameter of the eye equals the length of the snout, is two-sevenths 

 of that of the head, and a little more than one-half of the interorbital 

 space. The origin of the dorsal fin is midway between the root of 

 the caudal and the occiput, and corresponds to the thirteenth scale 

 of the lateral line. Origin of the anal opposite to that of the dorsal 

 (in the female). Dorsal fin of moderate size, anal small; caudal 

 scaly at the base only. Tail compressed, rather liigh, its least depth 

 being equal to the length of the head, without snout. There are 

 eight longitudinal series of scales on each side of the tail. Lateral 

 line rather indistinct. Greenish, each scale darker at the base. 

 Back of the tail with narrow, irregular silvery cross bars. 



The male has tbe dorsal fin somewhat elevated, but the longest 

 ray is scarcely as long as the head, without snout ; this fin is orna- 

 mented with round black spots. Anal fin modified into an intro- 

 mittent organ, and advanced to between the ventrals. Tail strongly 

 compressed, and comparatively higher than in the female. Caudal 



