NATURAL SCIENCES OF PHILADELPHIA. 203 



pair and geneials separated by a median longitudinal groove ; 

 latter plates 2.5 times as long as wide ; I'emaiuder of gular region 

 covered with small scales. Internasals together crescentic, the 

 points extending to behind the nostrils. Frontal broad cordate, 

 the apex posterior ; a half suture from the front divides it. Occi- 

 pitals narrow, length equal from muzzle to frontal, greater than 

 width of latter. They are separated by a single series of small 

 scales, in contact at one point. Gastrosteges 158, anal 1; uros- 

 teges 1 entire, 55 divided, and probably 10 wanting from the loss 

 of the extremit}^ The section of the tail is compressed, pentagonal. 

 Length, .381 M. ; to vent, .225 ; to rictus oris, .001. 



The ground color is brown, which is yellowish on the sides, 

 dark on the vertebral region, darker anteriorly, and almost black 

 on the head. The sides are marked from the second to the tenth 

 series of scales with dark brown 3-ellow bordered triangles, apices 

 upwards, three in an inch ; the bases scooped out and with the 

 legs sometimes cut off. A series of subquadrate blackish spots 

 separates their apices along the median line ; these sometimes 

 divide, and the halves alternate. Head unspotted, upper and 

 lower lips with lateral ventral groove ochre-j^ellow. Belly clearer 

 3'ellow, with several series of small deep brown marking. Outer 

 ends of urosteges blackish, anal shield black. 



The above description indicates how closely this serpent resem- 

 bles in coloration the j'oung examples of Trigonocephalus atrox 

 from the same country, and the T. neovidii of Brazil. This is so 

 marked as to constitute a case of mimetic analogy. But few cases 

 of mimicry of the Crotaline venomous snakes are to be observed 

 in South America, the imitations being chiefl}^ of the other venom- 

 ous group Proteroglyiyha, as represented by Elaps. In this con- 

 nection may be made a 



Reclamation, of the discovery of this, perhaps the most exten- 

 sive example of mimetic analog}' known in zoology. Alfred R. 

 Wallace, in his admirable work, " Contributions to the Theory of 

 Natural Selection," London, 1870,^ gives Dr. Giinther as his 

 authority for the facts of the case with regard to the genera Plio- 

 cercus Oxyrrhopiis, Erythrolamprus, etc., and refers to his own 

 previously published account of it in one of the British Reviews 

 for 1869. The first published account of the case will be found 



' Wallace is quoted by Darwin in " Descent of Man," to the same efffect. 

 1871.] 



