eigenmann: the FRESHWATER FISHES OF BRITISH GUIANA 109 



Charax gibbosus (Linnaeus), four specimens, 29 to 33 mm., Botanic Garden, 

 near Georgetown, British Guiana (C. M. Cat. No. 2940). 



Asiphonichthys hemigrammus Eigenmann, two specimens, 27 mm., Gluck 

 Island (C. M. Cat. No. 2138, 1. U. Cat. No. 12044); one specimen, 25 mm. (without 

 the caudal), Gluck Island (I. U. Cat. No. 12645), have archaic pectorals. One 

 specimen, 33 mm. (with the caudal), Gluck Island (C. M. Cat. No. 2941), has a 

 normal pectoral. 



In contrast to the species of Hyphessobrycon enumerated above we have one 

 thousand nine hundred arid ninety-nine specimens of Hyphessobrycon gracilis be- 

 tween 19-30 mm., all with normal fins. 



Whether any of the forms here enumerated are permanent, or simply abnormal 

 individuals, doomed to elimination, the interesting fact remains that a very unusual 

 mutation is arising simultaneously in widely different members of the same family. 

 This is of special interest in the case of the characins, for it seems quite certain that 

 other characters have independently made their appearance in different subfamilies. 

 A pair of conical teeth in the lower jaw belongs to this category. They are found 

 in widely distinct subfamilies both in Africa and America. A triple series of 

 teeth in the maxillary is another character that has been several times and inde- 

 pendently derived from a double series, and the double series from a single series. 

 The steps in this process have been preserved in part. The process in the latter 

 cases is again orthogenic, but it is doubtful whether progress is made by mutation. 



Changes of Color and Shape with Age. 



Marked changes in color take place with growth in Cichla. Only melanism is 

 taken into account. In the smaller specimens there is a series of three conspicuous 

 spots on the sides (Plate LXIX, fig. 1). These become ocellated a little later, at 

 the same time that vertical dark bands appear (fig. 2). With growth the two 

 anterior spots disappear entirely, the last one being retained as a caudal ocellus 

 (fig. 3). The sides are marked at this stage with three heavier, and a number of 

 fainter, cross-bands. With full growth the bands become concentrated into ir- 

 regular spots surrounded by lighter (fig. 4). 



Changes in the color of Crenicichla alia are sufficiently described in the diagnosis 

 of the species. 



The changes in color in Myloplus rhomboidalis and Myleus pacu are indicated 

 in Plates LVIII and LIX. In the figure of the adult M. pacu irregular black blotches, 

 which are frequently present, are not indicated. In both these species there is a 

 notable change in shape with age. The young are much slenderer, depth 2.6 in 



