NATURAL SCIENCES OP PHILADELPHIA. 297 



The brown of the upper surface of the head is pale, and is varied by a few 

 irregular darker spots. Total length 30 in., tail 9 in. One specimen in Mus. 

 Acad. Nat. Sci. from Capt. Jno. Dow. Habitat San Salvador, Centr. America. 



This is a plainly colored species, resembling the cenchoa more than the 

 leucomelas. In a specimen which we regard as belonging to the former 

 from Trinidad, sent by Mr. A. H. Ruse to the Mus. Smithsonian, the spots are 

 large, forty-three in number on the body, bordered with darker. The lateral 

 borders of vertical plate are very convergent, almost continuous with the 

 latero-posterior. The fifth inferior labial is largest. The coloration of the 

 vertex, as represented imperfectly by Seba, consists of a chevron-shaped 

 brown band between the orbits, the angle directed posteriorly ; a light 

 Y-shaped figure enclosed by brown bands on the occiput and nape ; a shade 

 of brown upon the vertical plate. The punctulations of the belly are most 

 dense medially, forming a band. 



In the three species of Himantodes, the postabdominal plate is divided, and 

 the dentition dipsadine. In the two species here described, the scale pores 

 are single ;inH. cenchoal cannot discover them. 



Trimorphodon lyrophanes Cope. Lycodon lyrophanes Cope, Proc. Acad. 

 Nat. Sci. 1860, p. 343. 



Upon the species described as above, as congeneric with the Siphlophis 

 s c o 1 o p a x,* we now establish the genus Trimorphodon, diagnosing it as fol- 

 lows: Body elongate, compressed; head distinct, depressed. Posterior superior 

 maxillary tooth separate, grooved ; median teeth small ; anterior elongate, 

 spaced. Anterior mandibular longer than posterior. Pupil vertical. Nasal 

 plates two, loreals two, pre- and postoculars two or more. Scales of the me- 

 dian dorsal line small. Anal and subcaudal scutella divided. Scale pores 

 double. 



In Siphlophis the anal plate is entire, there is one preocular, and one loreal 

 plate. The median dorsal series of scales is larger. In Dipsadomorphus the 

 anterior teeth are not stated to be longer, the loreal and preocular plates are 

 single, the median dorsal row of scales is larger. The anal is entire, and, if 

 it be a valid character, the scale pores are single. 



The genus is nearly allied to Tripanurgus and Siphlophis. The physi- 

 ognomy of the species is repulsive. The present species has only as yet been 

 certainly ascertained to inhabit Lower California ; the identity of specimens 

 from Arizona I regard as not ascertained. Mus. Acad Nat. Sci. and Smith- 

 sonian. 



Trimorphodon bi.scutatus Cope. Dipsas biscutata, D. & B vii. 1153. Dip- 

 sadomorphus biscutatus, Gthr. Cat. Colubr. Brit. Mus. 176. 



This species has the scales in twenty-five rows (23 D. & B.) the preceding, 

 twenty-one. Here the preocular is in contact with the vertical ; in the former 

 not. This has the head bands in chevrons, the lyrophanes, lyre-shaped ; 

 the dorsal spots are also much more emarginate anteriorly, laterally, and 

 posteriorly. The biscutatus is much the larger animal of the two. One 

 specimen (5569) in the Mus. Smithsonian was obtained near Realejo, Nicara- 

 gua, by Capt. J. M. Dow. 



Tropidonotus dimidiatus Boie, Isis von Oken, 1827, p. 535. Specimens 

 of this forgotten species have been obtained near Jalapa by Mr. Pease, and sent 

 to the Mus. Academy. It is related to the T. G r a h a m i i Gthr., but wants the 

 dorsal bands, and those margining the abdomen. The plumbeous of the 

 superior regions extends to the first row of scales, (third in G r a h a m i i ), 



* As Fitzinger's Neue Classification antedates Boie's memoir in the Isis von Oken, a 

 strict application of the law of priority requires that the Lycodon uni color of the 

 former work ( Boaodon D. & B.) should retain its name, while the scolopax receive 

 that of Siphlophis, Fitz. 1843. 



1861.] 



