112 Field Museum of Natural History — Zoology, Vol. X. 



cc. Origin of dorsal slightly behind to well in advance of anal. 



e. Origin of anal under or slightly in advance of dorsal; origin of 

 dorsal fin nearer tip of caudal than snout. 



f . Anal ^vith a black blotch at base of anterior 5 rays to tip of third 

 ray; dorsal rays 9 or 10. Priapichthys olonihia. 



ff. Anal without dark blotch at base of anterior rays; dorsal rays 

 10 to 12. Priapichthys annectens. 



ee. Origin of anal below middle of dorsal; dorsal rays 11 or 12; an 

 interrupted dark lateral stripe. Pseudoxiphophorus terrabensis 



eee. Origin of anal below anterior fourth of dorsal; origin of dorsal 

 nearer tip of snout than end of caudal. 



g. A series of short, dark, vertical bars along the middle of the side; 

 dorsal with 2 or 3 series of dark spots. 



Brachyrhaphis rhabdophora. 

 gg. A few faint, narrow, dark bars on posterior half of body; basal 



third of dorsal black. Brachyrhaphis umbratilis. 



aa. Dentary bones not firmly united, teeth movable; alimentary 



canal longer than the body, 

 h. Origin of the dorsal fin nearer tip of caudal than end of snout, 

 i. Origin of dorsal behind that of anal, nearer tip of caudal than 



end of snout, midway between anterior margin of eye and tip 



of caudal fin; origin of anal in advance of dorsal; anal rays 10. 



Pcecilopsis retropinna. 

 ii. Origin of dorsal over or before that of anal, 

 j. Origin of dorsal midway between base of caudal and anterior 



margin of the eye; modified anal of the male twice the length of 



head. Pceciliopsis pittieri. 



jj. Origin of dorsal midway between base of caudal and middle of 



opercle; scales with darker centers; modified anal of male short, 



its length less than that of head, 

 k. Base of dorsal rays ^vithout definite black spot; dorsal rays 9 to 



II, the free edge convex. Mollienisia spheitops. 



kk. A black spot at base of dorsal rays; dorsal rays 8 or 9; free edge 



of dorsal straight or slightly convex. Mollienisia s. tropica. 



hh. Origin of dorsal midway between end of snout and posterior edge 



of caudal fin, behind that of anal; anal rays 8. 



Mollienisia elongata. 



Alfaro Meek. 



Petalosa Regan, Ann. & Mag. Nat. Hist., 1908, 458 (type Petalosa 

 cultratum Regan). 



