24 Kobert E. Coker. 



Sometimes the marginal series shows a reduced number of scutes. 

 Thus ISTos. 4 (Fig. 20) and 8 had only eleven pairs of marginal 

 scutes, the eleventh marginals being very long. No. 245 had oidy 

 eleven on the left side (Fig. 18) and the two posterior scutes of the 

 left side, taken together, are equivalent in size to the last three on 

 the right. Partial fusion of 11 and 12 (K) was noted in ]^o. 47 

 and of 2 and 3 (R) in No. 176 (Fig. 34). In Nos. 153, 174 and 

 185, the twelfth marginals were reduced in size, and, in the latter 

 two specimens, were asymmetrical (Figs. 26 and 29). 



Nuchal. 



The most interesting abnormalities of scutes are those shown by 

 the nuchal and the neurals. The most anterior of the median scutes 

 of the carapace is always given the name nuchal, but is generally 

 included with the other median scutes in the neural series. It resem- 

 bles the other neurals in being median and usually unpaired, but 

 differs from them in some evident respects. Its direction of pre- 

 dominant growth is the reverse of that of the other median scutes. 

 It is absent in some existing species and in the fossil turtles of the 

 genus Pleurosternum Owen, belonging to the sub-order amphi- 

 chelydia Lydekker, a group which von Zittel regards as ancestral to 

 the modern Pleurodires and Cryptodires ('02). I find it occurring 

 in paired condition or marked with a median funwv much more 

 frequently than any other commonly unpaired scute of the carapace. 

 In this connection the frequent evagination of this scute in Clem- 

 mys guUatus is of interest. 



The nuchal was represented by a pair of scutes in ten specimens: 

 Nos. 44, 74, 78, 97, 124, 168, 196 (Figs 31), 200, 210 (Figs. 

 5 and 17), and 228 (cf. also Table Y, Nos. 244, 245 and 249, 

 and figures). A distinct median furrow, not distingiiishable as a 

 seam, occurred in nine individuals: Nos. 3, 73, 116, 125, 182, 185, 

 208, and 211 ; a faint median furrow was observed in No. 80. 



Costals. 

 It will be observed that abnormal scutes occur much more fre- 

 quently in the posterior costal region than in the anterior. 



