3i 8 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. X. 



dividuals than others; sides with more or less distinct dark spots. In 

 the specimens in which they are most distinct they form short, vertical 

 bars, and in others they appear as quadrate spots. Dorsal fin with 

 black chromatophores preceding each ray, forming a dark bar near the 

 base; interradial membranes between the posterior rays of anal with 

 black chromatophores, forming a dark spot at base of fin, these chro- 

 matophores may or may not be extended on the rays and up the fin. 

 All intergradations from an obscure spot at base of the rays to a promi- 

 nent spot, with the black extending nearly to the tips of the rays, occur. 

 A fairly common species on both slopes of Panama, occurring mainly 

 in the upper courses of creeks. Numerous specimens are at hand. The 



FIG. 5. DISTAL PART OF INTROMITTENT ORGAN OF Gambusia tpiscoti Steindachner. 



(Greatly magnified.) 



largest female is 52 and the largest male 23 mm. in length. It was not 

 taken in the Rio Tuyra or Rio Bayano basins. 



Further study of our material convinces us that the form we de- 

 scribed as Gambusia latipunctata in 1913 intergrades with the present 

 species and is therefore not valid. 



Habitat: Both slopes of Panama, north of the Rio Bayano. 



56. Gambusia cascajalensis Meek & Hildebrand. 



Gambusia cascajalensis Meek & Hildebrand, Field Mus. Nat. Hist. 



Pub., Zool. Ser., X, 1913, 86 (Rio Cascajal, Porto Bello, Panama). 



Head 3.2 to 3.9; depth 3.7 to 4.5; D. 7 or 8; A. 10; scales 28 to 30. 



Body rather slender; the profile straight over the head, slightly 

 convex from nape to dorsal; head rather flat above; snout moderate, 

 3.1 to 3.35 in head; eye 2.8 to 3.25; interorbital 2.1 to 2.4; mouth rather 

 small, the cleft extending about one-third the distance to eye; teeth in 

 the jaws pointed, in bands, the outer ones slightly enlarged; scales 

 moderate, cycloid, extending forward on snout and on base of caudal 

 fin, 7 longitudinal rows between anterior part of base of dorsal and base 

 of anal; caudal peduncle strongly compressed, its least depth 1.7 to 2 

 in head; origin of dorsal in female over posterior rays of anal, and about 

 midway between middle of eye and tip of caudal, in the male its origin 



