206 PROCEEDINGS OF THE ACADEMY OF 



On three new forms of Rattlesnakes. 

 BY ROBERT KENNICOTT. 



Caudisona 1 e p i d a Kennicott. 



Spec. char. Head ovoid, tapering to the nose, which is very narrow, pointed 

 and much depressed. Nostril very small, circular and placed near the point of 

 the nose in about the middle of a single nasal. Two elongated frontals in 

 contact, extending behind the nostrils. Superciliaries and other large plates 

 smooth. Rostral sub-triangular, broader than high, the apex turned back 

 slightly upon the crown. Upper pre-orbital small and separated from the 

 post nasal by the width of two larger plates. Labials rather large, 12 above 

 10 12 below. Color of head yellowish ash. 



Two heads of a rattlesnke from Presidio del Norte and Eagle Pass show such 

 remarkable features as to render it justifiable to describe the species from 

 these alone. 



The head is much depressed, the general outline ovoid, tapering regularly 

 from about opposite the angle of the mouth to the nose. The crown is remark- 

 ably smooth and the occipital scales very faintly carinated. There are two large 

 frontals elongated laterally and posteriorly, with their inner ends in con- 

 tact. They are convex on their external, and concave on their internal edges, 

 and extend for nearly half their length back of the nostril. Behind and fitting 

 into the emargination formed by these, are two subquadrangular and smaller 

 plates in contact ; immediately behind these is another similar pair. On 

 each side of these two last pairs, at the edge of the crown, between the super- 

 ciliaries and anterior frontals, is a larger plate. The superciliaries are rather 

 small, and, like the other larger plates quite smooth ; the space between 

 the superciliaries is narrow, and filled with irregular rather large scales ; the 

 posterior part of the crown is also covered with rather large and smooth scales. 

 The pre-orbitals are remarkable ; the lower is, as usual, small and elongated 

 over the pit, but the upper, very small and quadrangular, is separated from 

 the nasal by the length of two plates, each larger than itself. In all the other 

 species the upper pre-orbital is large, more or less elongated and in contact 

 with the post nastal or only separated from it by the width of one smaller 

 plate. The sub-orbital chain is complete, and there is only a single row of 

 scales between it and the labials. The color of the head is uniform yellowish 

 or light brownish ash without any distinct spots or stripes, though each plate 

 is minutely mottled with brownish, and with a few scattering large black dots, 

 and there is very faint indication of the usual posterior facial stripe extending 

 over the angle of the mouth. 



The body of this species will doubtless exhibit characters as important as 

 those of the head. It will at once be distinguished from C. molossus and 

 C. tigris by the single nasal, position of pre-orbitals, number and compara- 

 tive size of labials, and number of rows between the sub-orbitals and labials, 

 and by the narrow pointed nose instead of the broad blunt snout of C. 

 molossus and C. t i g r i s. It disagrees also with C. 1 u c i f e r in all of the 

 above characters, excepting the size of labials and the narrow nose, and differs 

 widely from that species in the depressed snout, wide rostral, and perfectly 

 smooth plates and scales on the head. By the smoothness and size of the 

 plates, and absence of the horn, it will at once be distinguished from C. 

 cerastes. It will be impossible to confound it with any of the eastern 

 species. 



Caudisona a t r o x Cope. Var. Sonoraensis Kennicott. 



Specimens from Sonora and vicinity show some permanent differences from 

 the more eastern types ; and, though the differences detected as yet are 

 thought too slight to characterize a distinct species, subsequent researches 

 with the aid of better material will very likely prove the western type to be 



[Aug. 



