340 



Mr. C. T. Re^an on the 



Placodermi. 



Tlie close relationship of the Coccosteidie and Asterolepidai 

 jiad 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 

 leleostomi. It has b:'en stated that the bones of the skull 

 of the Coccosteidaj cannot be homologized with those of 

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

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



Fiy. 3. — Diag-rauis to show the arraugement of the boues of the cranial 

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

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

 I.O., lateral dermal occipital; p., parietal ; /., frontal ; ptf., post- 

 frontal ; s.t., supratemporal ; ^;2n., pineal ; etk., ethmoid ; pinx., 

 prffimaxillary ; so., suborbital ; oj)., 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 Ehizodontidag 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. 



