"ABNORMALITIES" IN CHELONIA. 69 



etc., of these species, involving the collection of large numbers of 

 individuals of all sizes. One of the most striking phenomena 

 that came to light was the prevalence of many kinds of scute 

 abnormalities, consisting for the most part of supernumary scutes 

 on the carapace and plastron. As examples multiplied I became 

 aware of a marked degree of regularity in these abnormalities, 

 the same supernumerary scutes occurring in exactly the same 

 locations time after time. 



Diversity in scutes had been noted by two observers. Gadow 

 ('99) studied Tlialassochelys carctta (L.), a species with no fixed 

 number or arrangement of scutes, and Parker ('01) found two 

 abnormal specimens of Chelopus insculptus (Le C.) on the basis 

 of which he published a paper on correlated abnormalities in the 

 scutes and the bony plates. 



It seemed, then, that this phenomenon needed further investi- 

 gation and the collection of large numbers of abnormal speci- 

 mens was begun in the hope of reaching a rational explanation 

 of this very prevalent diversity. Careful study has convinced 

 me that these abnormalities are to be considered not as meaning- 

 less anomalies but as examples of systematic atavism in the sense 

 of deVries. From this standpoint it seems possible to throw 

 some light on the phylogeny of Chclonia. 



The color patterns are intimately associated with the scutes 

 and throw much light on their phylogeny. Consequently a brief 

 consideration of chelonian coloration has been appended. 



2. Nomenclature. The Normal Plate and Scute Pattern. 



The following description and appended drawings (Plate I., 

 Figs, i and 2), although referring particularly to an adult female 

 specimen of Graptemys geographica, will apply to any genus of 

 the Emydidae. Fig. I represents the dorsal and Fig. 2 the ventral 

 aspect. 



The armor of tortoises consists of two elements, bony plates 

 and horny scutes, which for brevity will be referred to as plates 

 and scutes. Dotted outlines are used for the plates and solid 

 outlines for the scutes. In labeling, small letters are used for 

 plates and capital letters for scutes. 



A. Plates. There are in the carapace (Fig. i) five longitudinal 



