Classification of the Order Ostario^ohysi. 



19 



The African genus Hydrocyon has most of the characters 

 of Characinfc such as Afestes, from which it differs especially 

 in the structure of the mouth. The well-developed maxillary 

 is firmly united by suture to the prsemaxillary, and the latter 

 is movably articulated with the ethmoid. The jaws are not 

 much produced and the teeth are strong spaced canines ; the 

 mouth can be widely opened, and by pulling down the lower 

 jaw the upper can be readily made to move in a vertical 

 plane until the edge forms an angle of 50° with its position 

 when the mouth is closed *. 



Family 2. Gastropelecidae. 



The South- American genus Gastropelecus has usually been 

 placed near Chalcinus, but I find that whilst the latter is 



Fig. 1. 



Oleithriim and primary pectoral arch (except radials) of 

 A, Gastropelecus pectorosus and B. Chalcinus trachypornus. 



cl, cleithrum ; cor, hypocoracoid ; sc, hypercoracoid (scapula) ; 

 m, raesocoracoid. 



extremely similar to Brycon in osteological characters, Gastro- 

 pelecus is quite different. Gastropelecus is remarkable for its 



* According to Boulenp^er (Cat. African Freshwater Fishes, i. p. 179) 

 the preemaxillaries are " slightly movable vertically." 



2* 



