26 Eobert E. Coker. 



arbitrary. They are based on the fact that the seam between C4 

 and ]Sr5 typically meets Mil at a point near the middle or anterior 

 part of its inner border (Fig. A, etc.). 



1. (a) 111 a specimen with the usual number of twelve mar- 

 ginals, any scute in order with the costals which does not extend 

 positively beyond Mil is considered a costal. This rule certainly 

 becomes arbitrary when applied to small scutes which extend neither 

 anteriorly nor posteriorly to Mil, and which may, therefore, be as 

 much within the neural region as within the costal region (PI. VII, 

 Fig. 21). It is convenient, however, to class such elements with the 

 costals. 



Compare : 



much within llic neural region as within the costal region (PI. IV, 



ig. 21, small scute, right side 



ig. 10, small scute, left side 



Ig. 16, large scute, left side* 



ig. 46, large scute, right sidef 



Ig. 44, medium scutes, both sides 



ig. 50, small and medium scutes, left side 



ig. 14, medium scute, left side 



ig. 39, small scute, right side 



ig. 23, medium scute, right side 



ig. 27, LC4 represented by two scutes 



(b) Sometimes extra marginals occur in association with extra 

 costals; in such cases, the costal region may be supposed to extend 

 to the twelfth marginal, which is the next to last, as is the eleventh 

 in the typical series. Therefore, if there are thirteen marginals, a 

 scute in order with the costals, which does not extend posteriorly 

 to M12, is classed as a costal. 



Compare : 



No. 151, Pl{vn}^^S-{l5'} ^^^'^^ ^^"*^' ^"^^^* ^^^^* 



No. 196, PL IX, Fig. 42, ' medium scute, left side 



No. 198, PI. X, Fig. 45, small scute, each side 



No. 255, PI. IX, Fig. .39, small scute, left side 



No. 256, PI. VII, Fig." 23, small scute, left side 



2. If, in a specimen with twelve marginals, a scute in order 

 with the costals extends barely over on M12, but in its anterior 



*In the left costal series of this specimen, the supernumerary costal may, 

 of course, be one of the more anterior scutes. 



fNo. 217 is incorrectly included in this list. It may properly pertain to the 

 next list (b), but is a very doubtful case. 



No. 257, PI. VIII, F 



i 

 i 



