6 MEMOIRS OF THE CARNEGIE MUSEUM. 



Spintherobolus the suborbitals are feeble, very different from those in the other 

 genera. In Mixobrycon there is a naked area around the entire distal edge of the 

 third suborbital, similar to that in most of the Tetragonopterinse. The greatest 

 difference in the armature of the cheeks occurs in the postorbital region. In 

 Aphyocharax there are two postorbitals. Of these the upper is minute and neglig- 

 ible, the lower is large, convex, similar to the third suborbital, and covers the entire 

 postorbital area. Prionobrama has a similar arrangement. In other genera there 

 are three or more postorbitals and there is a wider or narrower naked area between 

 them and the vertical limb of the preopercle. In one genus, Aphyocheirodon, 

 there is considerable individual variation in the number and size of the postorbitals. 

 Anal fin. — The anal varies. In Cheirodon annce the base is very short, entirely 

 behind the dorsal, the margin is rounded, and the highest rays extend beyond the 

 tip of the last. In Paragoniates, Leptagoniates, and Phanagoniates the base is very 

 long, having its origin below the first dorsal ray or far in front of it. In Prionobrama 

 its margin is extremelj'^ falcate. Between these extremes there are various modi- 

 fications, the rays varying from twelve in Spintherobolus, fourteen in Leptobrycon, 

 Cheirodon annw, and Cheirodon pisciculus, to fifty in Paragoniates alburnus, and 

 seventy in Leptagoniates. In the great majority of species the number of rays 

 ranges between twenty and twenty-six. In the genus Cheirodon, the species of 

 which fall into two groups, the greatest range is from twelve to twenty-seven. 

 In C. pisciculus and C. annce the number of rays ranges from twelve to fifteen; 

 and in the nine other species from seventeen to twenty-seven. In seventy-nine 

 specimens of one species, Cheirodon interruptus, the number of anal rays is as follows: 



Number of rays: 17, 18, 19, 20, 21, 22, 23, 2^ 



Number of individuals: 2 6 28 16 12 11 3 1 



These are from several distinct localities, and the extremes have not been 

 observed in specimens from one locality. 



Dorsal fin. — The variation of the dorsal is not nearly as great as that of the 

 anal, and therefore of less taxonomic importance. Usually its origin is a little 

 behind or in front of the middle of the body, the distance in either direction being 

 negligible, but in Grundulus and in Prionobrama, Paragoniates, Leptagoniates, and 

 Phanagoniates it is distinctly behind the middle. Its outline may be rounded, ob- 

 liquely truncate, or it may be distinctly falcate as in Parecbasis. It reaches its 

 extreme development in Megalamphodus megaloptertis. 



Mouth. — The greatest evolution in this group, as in the rest of the Characins, 

 has taken place in the mouth and teeth. The mouth ranges in size from such a 

 minute affair as is found in Oligobrycon microstomus, Compsura heterura, Cheirodon 



