678 NOETH AMERIC;AN snakes COPE. 



a a Scales in nineteen tows. 



Robust; preoculars two ; loreal sboi-t ; parietal ([uite or nearly touching post- 

 ocular ; cross-bands much wider than interspaces ; a postocular stripe. 



S. nigrofasciatum * Gthr. 

 II. Superior labials seven. 



Robust; scales nineteen rows; preoculars two; pale brown, with sevenil 

 rows of small blackish spots ; a blackish half collar above ; head paler; 

 no postocular baud *S'. pacifieum t Cope. 



Sibon septentrionale Kennicptt. 



Dipsas septentrionalis Kennicott. U. S. Mex. Bound. Snrv., Reptiles by Baird, n, 

 p. 10, PL 8, Fig. I. Sibon annidatam septentrionale Cope, Checic List Batr. Rept. 

 N. Amer., 1875, 38 ; Catal. Batr. Rept. Ceutr. Araer. Mex., I8d7, G7. 



The largest species of the genus, ranging from Panama to Cameron 

 County, Texas, inchisive. 



TRIMORPHODON Cope. 

 Proc. Acad. Phila., 1861, p. 297 ; Bull. U. S. Nat. Mus. 32, 1887, p. G8. 



Posterior maxillary tooth elongate, grooved ; anterior teeth of both 

 jaws elongate; intermediate teeth of the maxillary series, shorter. 

 Head plates normal ; two nasals ; two loreals, one in front of the other. 

 Pupil vertical. Head very distinct. Scales smooth, subequal. Anal 

 scutum divided ; subcaudal scuta in two series. 



This genus includes species which inhabit Central America, Mexico, 

 and the adjacent parts of the United States. It is allied to Sibon, from 

 which the elongate anterior teeth and the two loreal scuta distinguish 

 it. No species of Sibon is known to possess two loreals, one anterior 

 .to the other. The species of Trimorphodon, with their wide triangular 

 head, narrow neck, and slitlike pupil, considerably resemble venomous 

 snakes, which their pugnacious disposition does not diminish. They 

 differ as follows : 



I. Scales in twenty-one rows ; superior labials nine. 



Head with brown chevrons above ; nape with a brown collar ; back with dia- 

 mond-shaped spots T. lambda Cope. 



Head with a lyre-shaped pattern above, nape with parallel stripes; dorsal spots 

 in pairs T. li/rophanes Cope. 



II. Scales in twenty-three rows; superior labials seven. 



Top of head black witb a white T-shaped spot; dorsal spots entire transverse 

 diamonds T. tan Cope. 



III. Scales in twenty-three (4) rows; superior labials eight. 



Top of head brown, with a small Y'-'^^'^P^f^ mark ; dorsal spots transverse dia- 

 monds, more or less transversely divided by paler ; nape with a brown 

 collar T. upsilon Cope. 



* Leptodira vifirofasciata Gthr., Ann. Magaz. Nat. Hist., 1868, 425. L. mystacina 

 Cope, Proc. Amer. Philos. Soc, 1869, p. 151. Dr. Giinther describes a specimen in 

 whicb the inferior preocular is abnormally absent or he has overlooked it, aud the 

 inferior postocular is wanting. My type is abnormal in lacking a labial, and in having 

 a temporal in excess. My specimens, five in nuuiber (mostly normal), are from the 

 west coast of Mexico (Tehuantepec) and Central America. 



] Leptodira pacijica Co^^e, Proc. Acad. Phila., 1868, 360; Mazatlau, Mexico. 



