?2 



G. J. de Fejervary: 



mably be regarded as primary and very specialized features, 

 unhomologizable with the skeletal elements of any higher Verte- 

 brate. The dermal bones of the skull of the fourth Order, the 

 Arthrod ira, are much like those of the more recent Fishes, with 

 which they may, to a certain extent, be successfully homologized. 

 They are, as may be stated for the dermal bones of the skull in the 

 great majority of the forms belonging to this Class, elements of a 

 primary exoskeleton. 



On account of this far-reaching morphological and phylo- 

 genetical dissociation existing between the Orders Osteostraci and 

 Antiar chi on one hand and the Orders Arthrodira, Elasmohranchii, 

 Acanthodei and Teleostomi cn the other, I propose to conserve, for 

 the formers, the ancient Subclass Placodermi (Agassiz), to which, 

 provisionally, the Anaspida might also be referred, whilst esta- 

 blishing for the latter 4 Orders the new Subclass Coinocrania."^) 



In the Batrachians the dermal ossifications of the skull 

 are, with relatively rare exceptions, represented by derivatives of 

 a primary exoskeleton. The skull of the Stegocephalia, which 

 are the prototypes of ,,armoured" Batrachians, presents easily 

 homologizable dermal bones, which seem to be all of a primary 

 exoskeletal origin. There exists, however, in this Order, an im- 

 portant osteological feature which must be here taken into consi- 

 deration. The roof of the skull of numerous Stegocephalians is 

 very rough. The asperities occurring on it are often very like a 

 „crusta calcarea". As the corium of the Stegocephalians secreted 

 lime in large quantities, it is not impossible that, at least in some 

 cases, such asperities were formed by lime - concretions 

 of the derm, having been deposed upon the primary dermal bones 

 of the skull. In this case the asperities would effectively result in 

 being a true ,, crusta calcarea", which would represent, on the 

 skull, the primitive stage of the form^ation of secondary 

 exoskeletal elements. 



We must not forget, however, that the ,,sculptures" observable 

 on the cranial bones do not ahvays necessaril}' represent a crusta 

 calcarea, i. e. a complex of secondary lime concretions, but are 

 often retraceable to the Osteogenesis of the respective bones 

 themselves, constituting thus their proper st ructura 1 feature. 

 This sculpture is radial, or concentric, or rather both.^) It is very 

 important to point out the fact that structural sculptures may be 

 present on both the primary and secondary dermal bones, so 

 that the mere presence or absence of sculptures offers no clue to 

 a distinction of these two skeletal components. 



') From y.oiiög = common, and rö y.Qaiiov = the skull. — Xot to 

 eonfound with the lacertilian group ,,Kionokrania" (from tö y.Uov — 

 eolumn, pillar). 



®) Cfr. F. Leydig, Üb. d. allgem. Bedeckungen d. Amphibien, Arch. 

 f. mikr. Anat. XII, Bonn, 1876, p. 77 of the Separate, dealing with the exo- 

 skeletal ossifications of Tarentola (Reptilia, Geckonidne). 



