340 



Mr. C. T. Re^an on the 



Placodermi. 



Tlie close relationship of the Coccosteidas and Asterolepida) 

 had been generally recognized until they were so widely and 

 unnecessarily separated by Cope, a proceeding which has 

 found more support than it deserved, and I have no hesitation 

 in uniting the groups of which these families are represen- 

 tative, together with the Osteostraci, in a single order of 

 Teleostomi. It has been stated that the bones of the skull 

 of the Coccosteidse cannot be homologized with those of 

 other Teleostomes ; but, as has recently been pointed out by 

 Jajkel*, if we take a generalized type such as Coccosteus, the 



Fig. 3. — Diagrams to show the arrangement of the bones of the cranial 

 roof in Coccosteus (A) and in a typical Crossopterygian {Rhizo- 

 dopsis) (B) (both after Traquair). m.o., median dermo-occipital ; 

 l.o., lateral dermal occipital: p., parietal ; /., frontal ; ptf., post- 

 frontal ; s.t., supratemporal ; pin., pineal; eth., ethmoid; pm.v., 

 prsemaxillary ; so., suborbital ; op., operculum. 



cranial roof-bones are arranged as in a generalized Crosso- 

 pterygian or Stegocephalian. Posteriorly we see the three 

 large dermo-occipital plates which we so frequently meet 

 with in the Rhizodontida? and Osteolepidse. In front of these 

 are the paired parietals and frontals, the latter bounding the 

 orbits laterally and partly separated medianly by a pineal f 



* Sitzb. Ges. naturf. Berlin, 1902, p. 103. 



t The pineal plate occupies the position of the pineal foramen of 

 some Osteolepids. 





