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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



grown forward into the space left between the maxilla and the orbit, and has become 

 subdivided into several bones. 



The mosaic of small bones on the cheek surely represents a fragmentation of the post- 

 orbital series of Lepidotus. That this fragmentation is secondary is indicated by the 

 presence of a plate corresponding in position to the normal undivided maxilla but here sub- 

 divided into six or more pieces which are fused with lateral line plates representing a 

 forward continuation of the suborbital series (Allis, 1905). 



The most notable features of the palate are the paired condition of the vomers (pre- 

 vomers) and the presence of paired, transversely extended articular facets (Fig. 25) on 

 either side of the mid-line, just in front of the cranial vault; the inner parts of these facets 

 are supplied by the parasphenoid, the outer by the prootics. They serve for the attach- 

 ment of the metapterygoids behind the mesopterygoids. These paired facets tie in the 

 long palate posteriorly and permit slight movements without loss of strength. 



The entire construction of lepidosteids indicates that these fish are descended from 

 short-bodied, short-mouthed forms in which both body and jaws became elongated antero- 

 posteriorly, thus transforming a peaceful nibbler into a predatory pike. Possibly the 

 labyrinthodont-like teeth of Lepidosteus may have been derived from stout, pebble-like 

 teeth which acquired pointed tips. 



The principal objection to this derivation is the fact that in the lepidosteids the 

 vertebras are highly perfected, completely ossified and opisthocoelus, while in the Mesozoic 

 protospondyls the notochord is persistent and the centra are at most ring-like. For this 

 reason several authors have placed Lepidosteus in an order by itself, the Lepidosteoidei. 

 But the students of amphibian and reptilian centra have shown, for example, that a 

 procoelous vertebra may become opisthocoelous by annexing the ossified intercentral ball 

 of the vertebra in front of it. At any rate, the perfection and specialization of the Lepidos- 



pmy 



Macrosemius 



Fig. 26. Macrostmius. After Smith Woodward. 



