CRANrAL OSTEOLOGY OF THE OSTEOGLOSSIDiE. 269 



SUMMAEY AND COMMENTS ON" THE SkULL IN THE 



Family Osteoglossid^. 



A review o£ the crauiological characters of the three genera 

 Osteoglossum (with Scleropaqes), lleterotis, and Arapaima shows 

 that they constitute a perfectly natural group. In shape and 

 general appearance the skulls vary considerably, but in the 

 more fundamental and essential featui'es they are similarly 

 constructed. 



In all three, the superficial parts of the bones are sculptured. 

 The parietal bones meet in the median line, and, as in the 

 widely remote genus Erythrinus, the deeper-lying, muscle- 

 covered hinder portion of each is not sculptured. The frontal 

 bones are relatively short and broad in Osteoglossum and 

 Seterotis^ but in Arapaima, with its elongated head, their pro- 

 portions are more normal. The nasal bones are large ; they 

 meet one another by a median suture, and they are suturally 

 united with the anterior ends of the frontal bones. 



The mesethmoid is small in all three genera. The opisthotic 

 is of fair size and touches the pro-otic. A subtemporal fossa 

 similar to that of the Elopidse and Albulidae is fouud beneath the 

 squamosal portion of the articular surface for the head of the 

 hyomandibular in Osteoglossum; in Arapaivia the subtemporal 

 fossa is wide and shallow, in Seterotis it is wanting. The basi- 

 sphenoid is wanting in all three ; the orbitosphenoid is a j^aired 

 bone in Arapaima, in Seterotis it is an imperfectly ossified 

 trough-like cartilage, in Osteoglosssum it is wanting. The occipital 

 half-centrum comes away readily from the basioceipital and 

 exoccipital bones, leaving their posterior ends rough, in Heterotis 

 and Arapaima, but not in Osteoglossum ; in Arapaima the centrum 

 behind the occipital half-centrum sends forward a pair of pro- 

 cesses which unite with the hinder part of the parasphenoid. 



The posterior temporal groove is completely roofed over in 

 Arapaima and Osteoglossum, but not in Heterotis; indeed, in 

 Heterotis the groove is barely recognisable. In all three genera 

 the parasphenoid bears on each side a stout peg which articu- 

 lates with the entopterygoid. In Osteoglossum Leichardti the 

 parasphenoid has an ascending process which reaches the 

 alisphenoid, and in Osteoglossum bicirrJiosum and Osteoglossum 

 formosum the corresponding process reaches the postfroutal. 

 The parasphenoid and vomer bear teeth in Osteoglossum and 



