106 Annals of the Carnegie Museum. 



tiidinally striate. As in other scales, this striation seems not to be 

 connected with the circuli, but in M. oligolepis it is clearly seen to be 

 connected with and derived from the minutely labyrinthine pattern of 

 the broad nuclear area, and this latter certainly results from modified 

 circuli. 



The genus may be divided into groups as follows: 



(fl) Group of M. oligolepis. 

 Moenkhausia oligolepis Giinther (Plate XXVII, fig. 3). Large scales 

 about six mm. long and seven mm. broad; base strongly bilobate in 

 middle (compare Leporiniis, etc.); circuli fine; radii very strong, 

 variable, about 5 to 10 apical, and one or tivo basal; nuclear area 

 broad, little below middle, with a minute labyrinthine or nodulose 

 pattern; laterobasal angles strong. 



(b) Group of M. lepidnlus. 



Scales much smaller, the largest {M. chrysargyrea) about three and 

 two-thirds mm. broad; pattern quite Hemigrammus-Vike, but with 

 the well-defined apical striation; radii about four to si.x, arranged 

 fan-wise; nucleus with well-detined pustuloid pattern. The species 

 are so much alike that no separate descriptions seem necessary. 



Moenkhausia chrysargyrea (Giinther). 



Aloenkhausia lepidurits (Kner). 



Moenkhausia collettii (Steindachner). 



Moenkhausia copei (Steindachner). 



Moenkhausia cotinho Eigenmann. 



Moenkhausia broivni Eigenmann. 



(c) Group of M. dichrourus. 



Moenkhausia dichrourus (Kner). Scales agreeing with the lepidurus 

 group, except that the radii (4 to 8) are arranged like straight branches 

 of a tree, leaving the main axis (the middle line) at angles of about 

 45°, only there is no actual median structure from which they arise. 



Moenkhausia grandisquamis (Miiller and Troschel). Scales of the 

 same type as M. dichrourus, but even more extreme, most of the 

 divergent radii becoming actually horizontal, transverse to the antero- 

 posterior axis of the scale, the upper ones are more oblique, and all 

 curve at the base, the whole i)attern resembling closeK' an English 

 peach tree trained against a wall. The transverse bars thus formed 



