VARIATIONS OK G ARTER-SNAKKS. 



49 



one specimen has been examined with more than 21-19-17 rows, 

 while about the City of Mexico and in Puebla a considerable propor- 

 tion have the reduced formula of 19-21-19-17, and in three specimens 

 from Veracruz one has 21-19-17, one 19-21-19-17, and the third 

 19-17, the smallest number for tlie species. It is also of interest to 

 note here that the type of Jlavilahris which was from Veracruz 

 (State) was said to have had 19 scale rows (Cope, 1866, 306). In 

 the diagram that constitutes fi<j;. 14 we have attempted to represent 

 <:;ra])hically this ^geographical variation in the number of scale rows. 

 The number of specimens at our disposal may perhaps seem too 

 small upon which to base conclusions as to the variations in the 

 numl)er of scale rows, since it has often been affirmed that the number 

 may vary a row or two in the same locality. Bearing in mind, how- 

 ever, the narrow limits of individual variation shown in our locality 



2i-23-2hl9-l7 



21-19-17 



,19-21-19-17 



19-17 



21 

 - — -:*:- - - 



'Pc 



35 





10 



-^l 



-ih 



Coyotes. Pat/.fu- \'icinity Puebla, 



Duraiigo; arc, of Puebla. 



Duraiigo. Michoa- Mexico 



cau. City. 



Veracruz 

 (State). 



Tucson, Coloiiia 

 Ariz. Juarez, 

 Sau All 

 drea,s, 

 Minaca. 

 Chihua- 

 hua; 

 Chihua- 

 hua. 

 Fig. J4.— Diagram shuwing the variation in the dorsal scale formula in Thamnophis 



megalops. 



records and indicated on our (hagram, it may be clearly seen, even 

 from this limited series, that, although slight, the decrease in the 

 number of rows from Patzcuaro southward is entirely definite; while 

 a similar reduction is indicated to the northward that may or may. 

 not be confirmed by larger series. 



In the number of labials, as in the case of the dorsal rows, the 

 question of sex may be ignored and the averages plotted directly, as 

 has been done on the diagram, fig. 15. By comparing the tables it 

 will be seen that although the arithmetical mean is quite constant, 

 it is not uncommon to find 9 supralabials and 10 infralabials in 

 Chihuahua; that no specimen north of Patzcuaro has been observed 

 w4th less than S, and that south of this locality 9 labials very seldom 



