CROCODILIANS, LIZARDS, AND SNAKES. 

 The genera of Dipsadinti; are distributed as follows: 



1101 



Paleotropical. 



Opiathoplus . 

 I)ipsas 



Passerita 



Gephyrinus 



Tragops 



Tropidococcyx 



Palearctic. 



Nearctic. 



■Neotropical. 



Ethiopian. 



Pytlionodipsas. 

 Dipsas. 



Khinobothryum 



Sibon 



Trimorphodon . . 



Dryopbis DryopbiH. 



Dr'yinus Dryiniis. 



TRIMORPHODON Cope. 



Trimorphodon Cope, Proc. Acad. Nat. Sci. Phila., 1861, p. 297; Bull. U. S. Nat. 

 Mus., No. 32. 1887, p. 68. 



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 Sibo7i, 

 from which the elongate anterior teeth and the divided anal scuta dis- 

 tinguish 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 21 (23) rows; superior labials nine. 



Head, with brown chevrons above ; nape with a brown collar ; back with diamond- 

 shaped spots T. lambda Cope. 



Head with a lyre-shaped pattern above; nape with parallel stripts; dorsal 

 spots in jjairs T. lyrophanes Cope. 



II. Scales in 23 rows; superior labials seven. 



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

 diamonds T. tan Cope. 



III. Scales in 23 (24) rows; superior labials eight. 



Top of head brown, with a small Y-shaped mark; dorsal spots transverse dia- 

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



T. tt2)silon Cope. 



IV. Scales in 23 (24) rows; superior labials nine. 



Top of head brown ; dorsal spots numerous transverse more or less divided dia- 

 monds T. collar is Cope. 



Top of head white, witli three round black spots; dorsal spot; few transverse 

 undivided black rhombs, with iiale edges T. villdusonii Cope. 



V. Scales in 25 (27) rows; superior labials nine. 



Top of head with chevron bands; dorsal spots formed of lour confluent spots 



and inclosing a palecenter T. biscittatus Dumeril and Kibron. 



Of the preceding species I have before nie one each of the T. lambda, tan, cuUarin, 

 and filkiiisonii. Of the T.hjrophanes there are six specimens; of the T. iipsilon nix, 

 and of the T. biscutatits four. 



The type of the genus is the T. lyrophanes. It is the only species 

 found within the limits of the United States. 



