362 NEW YORK STATE MUSEUM 



in the middle of the head above ; on either side of it are the super- 

 ciliary plates (s) lying immediately above the eye. The pair of 

 plates immediately in front of the vertical are the prefrontals (pf) ; 

 in front of these lie the internasals (af\ while the plate terminating 

 the muzzle, and lying in front of the prefrontals, is the rostral (r). 

 The plates behind the superciliaries and vertical are the occipitals (o). 

 The plates immediately behind the eye are the postoculars, or 

 postorbitals (po) ; those in front of the eye are the preoculars, ante- 

 oculars or anteorbitals (ao), in front of which are the loreals (lo). 

 Between the loreal and the rostral, and inclosing the nostril, are 

 the nasal plates (n). The superior labials (I) margin the upper 

 jaw ; the inferior labials (not marked in figure) margin the lower 

 jaw. The temporal plates lie between the superior labials and the 

 occipitals. 



The plates on the under side of the body, from the neck to the 

 vent, are the abdominal plates, or gastrosteges ; those from the vent 

 to the end of the tail are the subcaudal plates, or urosteges. The 

 anal plate is that immediately anterior to the vent. It may be 

 entire, or divided by a longitudinal parting ; and this difference is of 

 value in the determination of the various snakes, as will be seen by 

 reference to the artificial key to the genera (p. 364). The term, 

 " scales in . . . rows," will often be found in the specific descriptions, 

 the number of rows referred to in such case being the number of 

 longitudinal rows of scales, excluding the abdominal series. Keeled 

 or carinate scales show a ridge on the median line. 



Variation 



Of late years much attention has been paid by naturalists to the 

 subject of variation in animals, and certain relations between color 

 variations and geographic distribution seem to be well established. 



Certain species of snakes show variations in color and color pat- 

 tern to a remarkable degree, notable examples of this being the 

 common garter snake and the familiar, though somewhat scarcer, 

 milk snake. Prof. E. D. Cope paid particular attention to the vari- 

 ations in these species, and has discussed the subject in a long series 

 of papers several of which are cited in the accompanying reference 

 list (p. 357). As noted earlier in this bulletin (p. 359) the grouping 

 adopted in the present paper follows the views which he advanced 



