36 BULLETIN Gl, UNITED STATES NATIONAL MUSEUM. 



limits of the different forms. It may still be subject to modifications^ 

 however, that cause it to vary between the different forms. Should 

 such changes occur they may be conceived to take place in two ways — 

 either independently or dependently of the scale rows upon which 

 they are situated. If they are independent of particular scale rows, 

 changes in their position might take place either suddenly or gradu- 

 aWj. A gradual change ought to show forms that are characterized 

 by a different arrangement of the stripe intergrading with each other 

 in this regard, unless, indeed, they have since become distinct. An 

 examination of the intergrading forms, however, fails to reveal any- 

 thing of this nature. Thus, sirtalis-parietalis-concinnus , elegans- 

 ordinoides, and iwoximus-sauritus can be shown to intergrade along 

 their common boundaries, and yet there is no change in the position 

 of the lateral stripes, the intergradents being characterized by the 

 same arrangement of these bands. Similarly, also, in the case of the 

 forms now apparently isolated (megalops and hammondi, for example, 

 see pp. 123 and 137) the evidence of the other characters and of geo- 

 graphic probability point much more strongly toward a relationship 

 with the forms in which the lateral stripes have the same position than 

 with others. These evidences of relationship also argue against the 

 possibility of a sudden change in the position of the stripes as regards 

 the scale rows, for, as far as I can see, there is no evidence of rela- 

 tionship between any two forms with the bands on different rows 

 that is strong enough to require us to adopt this view for which we 

 have no direct evidence. This apparent constancy in the position 

 of the lateral stripes both within the different forms and between re- 

 lated forms gives strong support to the view that these bands are 

 closely associated with particular scale rows. 



Even if the lateral stripes are associated with certain scale rows, 

 however, there is still the possibility that their position may be 

 changed by the loss or addition of certain of these rows, but a mo- 

 ments consideration will show that the chance for any great modifi- 

 cation in this way is slight. At present, as we have seen, the fourth 

 is the lowest row to be dropped in the reduction in the number of 

 scale rows. The position of the stripe when on the second and third 

 rows can, therefore, experience no change in a decrease in the number 

 of scale rows from 23 to 15, the range of variation in the genUs, for it 

 is only the fourth, fifth, sixth, and seventh that are lost in this 

 reduction. 



In those forms in which the stripes are upon the third and 

 fourth there is also little chance for modification, for in but one 

 instance is the fourth row of scales dropped anteriorly to leave 17. 

 It is, however, in this group that most of the modifications in the 

 position of these stripes occur, and these variations are associated 



