CEOCODILIANS, LIZARDS, AND SNAKES. 773 



111 the R. n. Icennerlyi in three out of six specimens the parietal scuta 

 are shorter than the frontal. In sixteen of the H. n. nasicns, ten speci- 

 mens have the i)arietals shorter than the frontal. In the small number 

 of accessory scales the H. n. lennerlyi approaches nearer the H. sinius 

 than does the R. n. nasicus. The same affinity is indicated by the 

 smaller amount of black on the belly. It represents the genus in the 

 Sonoran region, while the R. n. nasicus occupies the Central. 



HETERODON NASICUS KENNERLYI Kennicott. 



Reterodon kennerlyi Kennicott, Proc. Acad. Nat. Sci. Phila., 1860, p. 336. 

 Heterodon simus kennerlyi CouES and Yarkow, Herp. Dak. and Mont, in Bull. 



U. S. Geol. Surv. Terrs., IV, 1878, p. 271.— Jan, Icon. Gen. Ophid., Pt. 10, 



pi. V, fig. 2. 



Head broad, very short anteriorly. Eostral plate very large. Loreal 

 plate very small, sometimes absent. Only two supplemental plates 

 behind azygos; the latter is sometimes replaced by two symmetrical 

 contiguous plates and without any supplemental The iuternasal and 

 prefrontal in contact with the posterior process of the rostral. Dorsal 

 row of scales twenty-three, all carinated except the first and second, 

 which are perfectly smooth. Ground color light yellowish-gray; a dor- 

 sal series of rather indistinct rounded or subquadrate brown blotches; 

 a second series of smaller circular spots much darker and more dis- 

 tinct; below this a third and more indistinct series. 



In its general form and appearance this resembles the Reterodon 

 nasicus nasicus, with which it is sometimes found associated. The body, 

 however, is rather shorter and thicker than in that form, and the head 

 is broader, with the part of the head anterior to the eye decidedly 

 shorter. The nasals are not as well develpped longitudinally as in R. 

 n. 7iasicus, but the result of this shortness of the anterior part of the 

 head is seen in the very small loreal, which is frequently wanting 

 entirely. There is never more than one loreal, while frequently two are 

 seen in R. n. nasicHs, in which the loreal is in every case strikingly 

 larger than in R. n. Icennerlyi. The most striking difference in these 

 species is in the number of small plates surrounding the azygos, or 

 postrostral. While in R. n. nasicus there are always at least ten of 

 these, one or two of which margin the inner edges of the ])renasals and 

 prefrontals, there are never more than two, and frequently but one, 

 additional plate in R. n. 'kennerlyi, and the prenasal and prefrontal are 

 always in contact with the posterior process of the rostral. The azygos 

 is short, nearly as broad as long, and usually there are just behind it 

 two contiguous plates of about the same size separating it from the 

 postfrontal, but not from the prefrontal. Frequently, however, the 

 azygos is longitudinally divided and ^vitll()ut any additional plates, but 

 in contact with the rostral anteriorly and the vertical posteriorly, and 

 not separated from the postfroutals. The frontal parietals, supercilia- 

 ries, and labials are much as in 77. //. nasicus, thougli generally less 

 developed longitudinally. The rostral is as large as in 77. n. nasicus. 



