THE TEMPORAL ARCHES OF THE REPTILIA. 



181 



ship of the turtles with the placodonts and plesiosaurs, but a 

 study of these forms convinces me that whatever resemblances 

 they may present can be accounted for by parallel development. 

 Briefly, there are other characters in the skeleton that seem 

 inconsistent with such a derivation from the Anomodontia, the 

 intercentral attachment of the ribs, the presence of parial inter- 

 centra in the cervical vertebrae of some forms, etc. The con- 

 clusion seems irresistible to me that the Testudinata represent a 

 distinct phylum of the reptilia, coordinate with the Synaptosauria 

 or Synapsida. 



By a sort of natural trephining of the skull- wall, a vacuity 

 appeared between the squamosal and parietal, the squamosal still 

 retaining its connection posteriorly with the parietal, and the 



FIG. 13. Placodiis, after Meyer. 



postorbital taking a part in the separated bar thus formed. This 

 is the condition in the Anomodontia and Sauropterygia, but never 

 in the Testudinata. In the Anomodontia and Sauropterygia, 

 concerning whose relationships there can be no doubt, the pro- 

 squamosals and quadratojugals have disappeared, leaving a single 

 bar composed of the squamosal, postorbital and jugal. It is also 

 assumed here that the prosquamosal and perphaps also the quad- 

 ratojugal have become fused with the squamosal, but of this there 

 is not a scintilla of evidence. A separate ossification, it is true, 

 has been said to occur in some plesiosaurs by Owen, 1 which 



Trans. Geolog. Soc. Land. (2), V., pt. iii., pi. XLV., 1840. 



