ON VARIATION. 29 



by fusion to form a vitta at first somewhat oblique, 

 but finally becoming nearly median. 



"The last two figures on the plate represent the 

 markings of gabbii (17) and saulcyi (18), in which the 

 ends of the bands or lunules are greatly prolonged. 

 The latter form, which represents dorsalis as well, is 

 but rarely seen so perfectly marked, the tendency being 

 toward a greater extension of the white. The other 

 species is scarcely variable, although equally a coast 

 form. 



"Those species which retain a permanent diver- 

 gence from the normal standard, such as togata (6) or 

 lemniscata (16), are doubtless descendants from a nor- 

 mal type which has varied, and in which a variety has 

 become isolated and perpetuated itself." 



The accompanying plate is copied from the original 

 drawing by Dr. Horn, and which accompanies the 

 paper now cited. 



b. Variations in the Osceola doliata. 



The Milk-Snake, Osceola doliata Linn., ranges in 

 North America over the Eastern, Central, and Austro- 

 riparian districts, and is absent from the Sonoran 

 and Pacific districts. It is found also in the humid 

 regions of Mexico and Central America, as far as the 

 Isthmus of Darien. Beyond this point it does not oc- 

 cur, but a very similar snake {Opheomorphus mimus') is 

 found in New Grenada. 



I have called attention to the color variations of 

 this species in a brief paragraph in the introduction to 

 my check list of Batrachia and Reptilia in North 

 America, 1875,' and have given the characters of the 



\Bulleiin Of the U. S. Naiimal Museum, No. I, p. 4. 



