THE AMERICAN TETRAGONOPTERINAE. 41 



ending in slightly enlarged scales, or the scales may become minute on the 

 caudal adhering and covering the lobes to a greater or less extent. The anal 

 may similarly have simply a basal sheath or may be covered to near its tip with 

 minute scales. 



The scales may be regularly imbricate or in certain regions there may be 

 interpolated rows. In some species there are but a few interpolated scales, 

 i. e., a single series becomes divided into two above the anal. The point of 

 division becomes more and more removed from the anal and the number of 

 divided series increases. In long slender species, or larger-scaled, deep species, 

 there are no interpolated rows. In deep, many-scaled species they sometimes 

 become numerous. Closely allied species or even varieties may differ in this 

 respect. In Astyanax fasciatus individuals with interpolated series are rarely 

 found except in the Rio Parahyba where the usual variety has been entirely 

 replaced by one with interpolated series. 



The dorsal is short, of between 9 and 12 rays, counting everything, and 

 its origin is usually in the middle of the body. The adipose dorsal is small 

 but almost always well developed. The caudal is always forked, the lobes 

 equal or subequal, rarely markedly different. The anal is another variable 

 element. Its origin usually below or behind the last dorsal ray may (Psello- 

 grammus and Phenacogaster) fall below its origin. Other things being equal 

 the deeper species have the larger number of anal rays. The number of rays 

 varies from 10 to 48. 



The reach of the pectorals and ventrals varies with the shape of the fish. 

 In deep species with long anal they overlap, in slender species they ordinarily 

 do not reach each other. The notable exception to this is found in Gephyro- 

 charax. 



The alimentary canal varies but little from the entire length of the fish. 

 There are a few pyloric coeca. 



The air-bladders are large, the posterior about twice the length of the 

 anterior, curved down behind in the deeper species. 



The range of color is limited. In life the caudal of the male is frequently 

 cherry-red, the dorsals and anal (and caudal in females) are frequently yellow. 

 A shoulder-spot of varying shape is usually present. There is usually a silvery 

 lateral band overlying a black band which becomes evident in formalin prepara- 

 tions. There is frequently a dark spot on the base of the caudal which is often 

 continued on the middle caudal rays. In Moenkhausia dichrourus and Brycona- 

 mericus exodon the tips or bands across the caudal lobes are dark. In Moenk- 



