12 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxin. 



others not. Whether some of the specimens of this species examined 

 are vsimply abnornal variations, whether the species is normally vari- 

 able in this respect or whether we are dealing here with a mutation in 

 the Devriesian sense still remains to be seen. If the species normally 

 varies in this respect it forms a bridge between Astyanax and Ileiiu- 

 granni)u>< and the latter must be merged with the former. (A similar 

 condition is found in MopnJchausia^ one of whose species, agassizi!^ 

 occasionally presents specimens with an incomplete lateral line.) For 

 the present the two genera may be kept distinct. The species of 

 Hemigramnius are all small, none of them reaching a length of 4 inches. 

 Most of them are much smaller. They are distributed from Oaxaca, 

 Mexico, to the Rio de la Plata and from Para to the Peruvian and 

 Ecuadorian Amazons. The}^ are not recorded from the Pacific slope. 

 As the species are all small we may expect many additions to the 

 genus. TI. lutheni^ H. unilineatus^ H. gj'acilis appear the most 

 widely distributed species, the first being recorded from Rio Grande 

 do Sul and the Paraguay Basin, the second from Trinidad to Bahia 

 and the last from the Rio San Francisco to the Amazons. Of the 

 19 species I have been able to examine all but elegans and rolnistulus. 



KEY TO THE SPECIES OF THE GENUS HEMIGRAMMUS. 



a Scales 30-36. 



h Dorsal conspicuously marked with a well-defined black spot; anal with definite 



markings. 



c A deep humeral spot; dorsal almost entirely black, middle caudal rays, last 



five anal rays and distal two-fifths of the remaining anal ra3\s black; D. 10 



or 11; A. 27 or 28; depth 2f-3; head 3i-3f ; eye 2f-2J; scales 6 or 7-33 



or 34-5 or 6, five scales with pores; maxillary with two teeth, each with 3 



points of nearly equal length. (Boulenger) callistus (Boulenger) 1. 



cc No humeral or caudal spots; a large black spot on the upper part of the 

 dorsal, sometimes obsolete; a narrow stripe of black from anus along margin 

 to the tip of the first anal rays; head 3.75; depth 2.75; eye 3 in the head; 



scales 6-34-5 ; five teeth in maxillary uniiineaius ( Gill ) , 2. 



bb Dorsal without well-defined markings. 

 d Anal with black markings. 



e A milk-white stripe on the fore edge of the anal, and a rather broad 

 violet stripe immediately behind it; a faint lateral l)and; A. 24; head 

 3i-3f ; depth 2|-2|; scales 5 or 5i-30 or 31-4. 



elegans, (Steindachner), 3. 

 (hi Anal without definite dark markings. 



/No humeral spot, caudal spot usually developed. (See ulreyi. ) 



g Maxillary without teeth; anal rays 17-19; height of anal nearly 

 equal to the length of its base; 4-7 perforated scales in the lateral 

 line; pectoral nearly to ventral; caudal deeply lobed; a large, 

 diffuse, dark caudal spot extends to the end of some of the rays 

 and fades out anteriorly; an inconspicuous silvery lateral band; 



depth 4; scales 32-30 to 32-2i nanns (Reinhardt),4. 



gg Maxillary with 2-4 conical or 3-pointed teeth. 



h No caudal spot, maxillary with two minute conical or slightly 

 notched teeth; dorsal and anal falcate, caudal widely forked; 



