4 Robert E. Coker. 



kempii Garman ; it is noted in several specimens of T. caretta, and in 

 other species J and a practically identical scute is iigured by 

 Boulenger for the remote species Chelodina novce-guinece Boulenger 

 (Boulenger, '89, PI. 5), but the author does not state whether or not 

 the presence of this scute is normal. There seems some ground for 

 the belief that such a definite recurrence of a scute of fairly regular 

 shape and position has some special significance. 



(c) In 3 of the above 31 turtles, the nuchal was represented by 

 a pair of scutes. The sanje abnormality occurred in 10 of 243 

 specimens of Malaclenwnys (Tables I-IV) and in 9 others the 

 nuchal, though unpaired, was marked by a median longitudinal 

 groove. This shield occurs in paired condition in several specimens 

 of Thalassochelys. In some species, notably in Chrysemys guttatus, 

 the nuchal often shows a distinct notch in the anterior margin. 



(dj In most genera of land and fresh-water turtles, axillary and 

 inguinal scutes are found anterior and posterior, respectively, to the 

 bridge and just beneath the marginals (Fig. B). These scutes are 

 regarded as the remnants of an ancestral series of infraonarginals 

 separating the pectoral, abdominal^ and femoral scutes of the plastron 

 from the marginals. Malaclemmys centrata has ''normally" only 

 the axillary, yet over 21 per cent, of 244 specimens examined, 

 possess inguinals, of varying size, on one or both sides. 



A number of other cases might be mentioned of recurring scutes 

 in definite positions in the neural, costal, and marginal series, but 

 these instances are sufiicient to illustrate the nature of the conditions 

 that have led some recent wl:"iters to assume that these abnormal 

 scutes are atavisms and that, as such, they have a comparative value, 

 similar to that of normal scutes, but of much more sigTiificance, since 

 they may point more directly to remote ancestral forms. 



Finally, it must be said that many other scutes are noted which 

 are not of these definite types, but which are perhaps not less sig- 

 nificant. 



In the present paper I will present my observations on the scutes 

 of two species of turtles, and then, in the light of these and other 

 observations, will inquire into the basis for an atavistic interpreta- 

 tion. It is necessary first to have in mind the phylogenetic sig- 



