"ABNORMALITIES IN CHELONIA. IOI 



that all these structures of the dorsal row, whether scutes with 

 bony cores, scutes without bony cores, or bony plates that have 

 been separated from their original scute coverings, are essen- 

 tially homogeneous, and that the differences seen in the differ- 

 ent regions are secondary or perhaps tertiary modifications. It 

 seems probable that the scutes at the posterior end of the row 

 represent the most primitive condition, which, through a process 

 of continuous variation have become more tubercular in form 

 and have acquired bony cores by the gradual ossification of 

 membraneous tissue. The three soft tubercles surmounting the 

 fifth to seventh vertebrae probably represent a reduced condi- 

 tion in adaptation to the fact that the base of the tail requires 

 flexibility and must be swung from side to side or partially with- 

 drawn under the carapace. The presence of such large promi- 

 nences as the bony tubercles would seriously interfere with the 

 mobility of the tail. The procaudal plates seem to have been 

 the last of the neural tubercles to have been flattened out to 

 form the dermal carapace. The last neural scute is probably the 

 original chitinous sheath of one of the procaudals, doubtless the 

 second one. The scute of the first procaudal I believe to have 

 been crowded out in the process of scute reduction that will be 

 discussed later. 



Over the 33 vertebrae there occur 27 structures of homogene- 

 ous origin, that may be designated scutes. This number is suffi- 

 ciently at variance with the number of vertebrae to preclude the 

 possibility that they have had a segmental arrangement. More- 

 over, their irregular arrangement and the dermal origin of the 

 bony cores make it certain that they are independent structures, 

 in opposition to views expressed by Gadow and others. 



An examination of the entire tail-trunk of another large speci- 

 men revealed the rather striking fact that the number of principal 

 rows of tubercles and large scutes in this region is identical with 

 that of the carapace and plastron, and that smaller, less regular 

 rows of tubercles and scales represent the principal lost rows. A 

 section of the tail-trunk was slit down the median ventral line and 

 flattened out for convenience in drawing, and from this the some- 

 what diagrammatic Fig. 5 5 was constructed. I was able with 

 certainty to homologize seven principal rows, three dorsal, two 



