350 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



Bilaterally Asymmetrical. 



It will be noted that in both these cases the asymmetry consists in 

 an absence of the VI row on the left side of the body. It is this row 

 that is normally added to the 19 row zone anteriorly and raises the 

 count to 21 rows. In the male the VI row exists on the right side 

 between the level of the thirty-third and the fifty-first gastrostege. 

 In the female this row is also present only on the right side ; it differs 

 in being interrupted, one series extending from the twenty-eighth to 

 the thirty-fourth, and the other from the forty-first to the forty-third 

 gastrostege. 



There is one important question bearing on these dermal characters 

 that requires to be settled, and that is whether the number and extent 

 of the scale rows are definitely fixed from birth and remain the same 

 throughout the life of the individual, or if their number and extent 

 may be increased as a sequel to abundant food, corpulency, preg- 

 nancy, and old age. The fact seems to be, that when a series of these 

 garter snakes from the same locaUty is examined, a suspiciously large 

 percentage of the low-scale row counts are foimd in the young and 

 haK-grown examples. 



OTHER VARIATIONS. 



All of the dermal characters show more or less variation. The 

 scale rows in the zones of transition from the neck to the body and 

 between the body and the tail are too irregular and compUcated to 

 permit the making of satisfactory records. There is some variation 

 m the size and shape of the rostral, frontal, and parietal shields that 

 depends upon the age of the specimen. The numerical variations in 

 other characters are very important to ascertain, for they confirm 

 beyond dispute, as Doctor Ruthven has demonstrated, the genetic 

 relationships among the species. 



Variation in Gastrosteges. 



Attention is drawn to the fact that the minimum and maximum 

 counts have been found in the female specimens. In the males the 

 range of variation is but 55 per cent of the total and centers nearly 

 around the mean for the series. 



