ABNORMALITIES IN CHELONIA. /I 



called SHpraiiMrginals. Traces of a median ventral row of scutes 

 are found normally in some species - - and I have given the name 

 " inter pldstral* to this row. A single median scute occurs 

 normally in the anterior part of the plastron of certain special- 

 ized groups and receives the name intergular. 



II. DISCUSSIONS OF THE PRESENT STATUS OF THE QUESTION 

 CONCERNING THE MORPHOLOGY OF THE CHELONIAN ARMOR. 



The frequent abnormal occurrence of traces of the inframargi- 

 nals and interplastrals in Grapteinys gcograpliica, Chryscinys mar- 

 gi/iataznd Chclydra scrpcntinaled me to review the literature re- 

 lating to the evolutionary history of the chelonian carapace and 

 plastron. 



For nearly a century the chelonian armor has offered to mor- 

 phologists a problem of unusual difficulty, and, although much 

 has been written on the subject, its derivation is still unsettled. 

 The question has been attacked from the three standpoints of 

 paleontology, embryology and comparative anatomy. 



I. Paleontological data are far from conclusive. It is not pos- 

 sible to go into this phase of the subject at all fully. Baur in 

 1887 published a brief summary of the more valuable paleonto- 

 logical data in an article entitled " On the Morphogeny of the 

 Carapace of the Testudinata." A brief statement of the substance 

 of this paper will, perhaps, serve to show the inadequacy of the 

 paleontological evidence in this case. 



The condition seen in the Dermochelydae is considered to be 

 the most primitive. Fossil remains of this gro^ip agree closely 

 with the existing Dermochelys coriacca in the possession of " a 

 pavement of small osseous plates extending over the whole shield, 

 jointed to one another by more or less fine sutures. The num- 

 ber of these plates is much larger than that of the other Testudi- 

 nata, which is never more than 70." This pavement of osseous 

 plates is not united with the internal skeleton, as are the plates 

 of other Testudinata, but has an independent dermal origin. 

 " That the carapace of the Dermochelydae is homologous to the 

 carapace, without internal skeleton, of the rest of the Testudinata, 

 there is no doubt." The fusion of the dermal pavement bones 

 with the ribs and vertebras is, according to Baur, proved by a 



