124 BAHIA BLANCA. 



degree independent of structure, has a tendency 

 to vary by slow degi'ees. The extremity of the 

 tail of this snake is terminated by a point, which is 

 very slightly enlarged ; and as the animal glides 

 along, it constantly vibrates the last inch ; and this 

 part striking against the dry grass and brushwood, 

 produces a rattling noise, which can be distinctly 

 heard at the distance of six feet. As often as the 

 animal was irritated or surprised, its tail was 

 shaken ; and the vibrations were extremely rapid. 

 Even as long as the body retained its imtability, a 

 tendency to this habitual movement was evident. 

 This Trigonocephalus has, therefore, in some re- 

 spects, the structure of a viper, with the habits of a 

 rattlesnake ; the noise, however, being produced 

 by a simpler device. The expression of this snake's 

 face was hideous and fierce : the pujail consisted of 

 a vertical slit in a mottled and coppery iris ; the 

 jaws were broad at the base, and the nose termi- 

 nated in a triangular projection. I do not think I 

 ever saw anything more ugly, excepting, perhaps, 

 some of the vampire bats. I imagine this repul- 

 sive aspect originates from the features being placed 

 in positions, with respect to each other, somewhat 

 proportional to those of the human face ; and thus 

 we obtain a scale of hideovisness. 



Amongst the Batrachian reptiles, I found only 

 one little toad (Phryniscus nigi'icans), which was 

 most singular from its colour. If we imagine, first, 

 that it had been steeped in the blackest ink, and 

 then, when dry, allowed to crawl over a board, 

 freshly painted with the brightest vermillion, so as 

 to colour the soles of its feet and parts of its stom- 

 ach, a good idea of its appearance will be gained. 

 If it had been an unnamed species, surely it ought 

 to have been called Diabolicus, for it is a fit toad 

 to preach in the ear of Eve. Instead of being noc- 



