310 



OS THE SKULL OF OSTEOGLOSSUM FORMOSUil. [Apr. 2, 



but, at the same time, it is equally clear that there can be no 

 direct phylogenetic relation between the two genera. Hence the 

 independent development of an essentially similar mechanism in 

 two such widely distinct fishes can only be regarded as an in- 

 teresting and striking example of parallelism in evolution. 



EXPLANATION OF PLATE XXII. 



[The figures are all of natural size.] 



Fig. 1. Lateral view of the hinder part of the skull of Osleoglossum/ormosum, 

 showing the lateral and articular processes of the parasphenoid and 

 the mesial cluster of parasphenoidal teeth. 



2. Ventral view of the same structures. 



3. Lateral view of the bones of the proximal portions of the mandibular 



and hyoid arclies, including also the proximal part of the lower jaw, 

 the hinder section of the maxiUa, and the articular surface on the 

 metapterygoid. The dotted line indicates the extent to which the 

 mesopterygoid and pterygoid bones overlap the inner surfaces of the 

 metapterygoid and quadrate respectively. The process of the hyo- 

 mandibular (ht/m.^) has been partially removed. 



4. Ventral view of the same structures, showing the two opposable series 



of mesopterygoid teeth, the parasphenoidal teeth, and the mode of 



articulation of the metapterygoid with the two lateral condyles 



furnished by the parasphenoid. 

 .'i. The oral surface of the "tongue," showing the three principal series of 



teeth, the attachments of the first three pairs of hypobranchial bones, 



and the second basibranchial element. 

 6. Similar view of the " tongue " of Lepidosteus osseus, showing the 



arrangement of the two rows of rugose plates, the attachment of the 



hypohyals, and the first basibranchial cartilage. 



