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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



paired posttemporal fenestrse. "One of the most striking and characteristic features of 

 the skull of Osteoglossid fishes," writes RIdewood, "Is the occurrence of a paired lateral 

 peg of the parasphenoid for articulation with the hyopalatlne arch, described by Bridge 

 In Osteoglossum formosum (Proc. Zool. Soc. London, 1895, pp. 302-310)." Bridge found 

 that "the linear series of obliquely set teeth in the two mesopterygoids of this fish become 

 opposable In the median line of the oral cavity and. In conjunction with the mesial teeth 

 on the parasphenoid, form part of an additional oral masticating mechanism." Bridge 

 compares this arrangement with the somewhat analogous conditions in the palate of 

 Lepidosteus, where there is a secondary facet for the metapterygold, at the junction of 

 processes from the parasphenoid and the prootic. RIdewood found the articulation in 

 question not only in all three species of Osteoglossum but also In Arapaima and Heterotis 

 (Fig. 58). Its presence in Pantodon constituted a striking evidence of the relationship of 



scalebone 



Heterotis niloticus 



Fig. 58. Heterotis niloticus. After Ridewood. 



that form to the Osteoglossldae. The rear view of the skull of Osteoglossum vajidelii (Fig. 

 57) shows that these diverging processes from the parasphenoid are also analogous with 

 the basipterygold processes of primitive amphibians and reptiles. They brace the ascending 

 dentlgerous processes of the mesopterygoids and transmit the upward thrusts from the 

 palate to the neurocranium. They are also attached to a pair of long, special and very 

 peculiar processes from the hyomandibulars, the existence of which Is difficult to account 

 for. Probably they represent an elongation of that process of the hyomandibular which 

 In other isospondyls is often found above the metapterygold. We may assume perhaps 

 that as the quadrate-articular joint grew downward, this supra-metapterygoid process of 

 the hyomandibular grew downward and forward, as if to brace the hyomandibular, until 

 it passed over the junction of the ento- (meso-) pterygoid and the ascending processes of 

 the parasphenoid. 



Another marked characteristic of all the Osteoglossldae is the fact, noted by RIdewood, 

 that the nasals are large bones which meet in a long suture In the mid-dorsal line and 

 widely separate the frontals from the mesethmoids, as in Amia. Examination of a para- 



