78 H. H. NEWMAN. 



such anomalies have been previously described, it seems worth 

 while to tabulate those in my collection - - an easy task in view 

 of the fact that the scutes occur in definite places. In any species, 

 such as Chelydra, that possesses this row normally, there are 

 typically three scutes in the row, one in contact with the axillary, 

 one at the angle of contact of the pectoral and humeral and the 

 marginals, and one abutting on the inguinal scute. These three 

 scutes may be designated respectively as I., II. and III. Out of 

 476 specimens of Grapteuiys geographica examined, I found 3 1 

 with traces of inframarginals varying all the way from three large 

 scutes on each side to one small one on one side. The tabula- 

 tion below gives the number of the specimen, the sex, the length 

 and breadth of carapace in millimeters, the occurrences of infra- 

 marginals on the right and left sides separately. Three general 

 sizes are distinguished, which although quite arbitrarily laid down 

 may serve to give a more definite idea of the amount of variation 

 that occurs. These sizes are designated as large, medium and 

 small. 



At Woods Hole this summer I found two specimens of Nan- 

 ncinys gnttata and three specimens of Chrysemys picta with well 

 marked inframarginals. 



It will be readily seen that in both species the middle scute is 

 much the commonest recurrence, and this is natural if we consider 

 that in Chelydra, and other species with well developed infra- 

 marginal rows, the middle scute is always the largest. The 

 largest and most vigorous scute would probably persist longer 

 and hence be most likely to recur as an atavistic reminiscence. 

 The fact that no. III. is next in prevalence in Grapteuiys and 

 no. I. in Chrysemyjs, indicates that the order of suppression of the 

 other scutes of the row was subject to individual and group 

 variation. 



In the species Chelydra serpentina the inframarginal row is in 

 a highly variable condition. Many stages in the reduction of 

 numbers of scutes are to be seen in different individuals. The 

 middle scute, corresponding to no. II., is always the largest, and 

 the adjoining ones are next in size and would correspond to 

 no. I. and no. III. Frequently there are two or three smaller 

 scutes both in front of and behind the large central scutes, but 



