244 Zoological Society : — 



brasiliensis ; but all these differences do not appear very striking in 

 Schlegel's excellent figures on plate 1 9 of the ' Essai.' My three 

 specimens distinct from C. atrox would rather agree in these points 

 with the descriptions of C. brasiliensis of these authors. 



Schlegel points to the larger size of the superciliary and superior 

 labial shields in C. atrox, to its larger and more numerous mental 

 shields, to the stronger keel on its scales, showing a strong tendency 

 to take the form of a tubercle, by which I understand that it is 

 higher and shorter, not reaching the tip. Now these characters, if 

 they occurred simultaneously, might very well serve as some of the 

 specific characters ; and it does not appear just in Dumeril and Bi- 

 bron to say (vii. p. 1508), " M. Schlegel, dans I'embarras oh. il s'est 

 trouve, n'a indique que des differences peu importantes, tirees de la 

 forme des ecailles dont la carcne parait plus forte ; des lames noires 

 alongees, ou de I'etendue relative des plaques surciliaires ainsi que les 

 plaques labiales," — although they confess their inability to suggest 

 any better characters, and still persist in considering them individuals 

 belonging to two species, having no other basis for their separation 

 than the frequent occurrence of C. atrox in Guiana, whilst the other 

 species is never found there. 



Comparing my three specimens, which differ from those of C. atrox 

 in the last-mentioned respects, and first as regards the size of the 

 superciliary shields, I cannot come to any very precise decision, as 

 they are not full-grown. Comparing with one another old and 

 young specimens of C. atrox, I find that not only the superciliary, 

 but all other head-shields are proportionately larger in young indi- 

 viduals, so is the pit in the cheek ; and the whole head is flatter, 

 especially the occiput, and more elongate in adult specimens. I 

 compared the three specimens with those of corresponding size of 

 C. atrox, but I could not arrive at any decided opinion ; and, con- 

 sidering the difference in size of the figures in Schlegel's plate 19, 

 they also do not allow me to draw any safe inference from the rela- 

 tive size of the superciliary shields in each species. Besides, I 

 am not acquainted with the absolute size each species may attain. 

 As regards the size and number of the mental shields, I cannot 

 find any very striking difference ; in some specimens of C. atrox 1 

 have found one, in others two, and even three pairs of chin- shields ; 

 in the three specimens which differ in other respects from them, 

 I always found only one pair. The labial shields are certainly 

 smaller in my three specimens which do not agree with C atrox. 

 But more striking still is the shape of the scales and their keel. 

 The three specimens I am inclined to regard as referable to C brasi- 

 liensis have narrower scales, their keel lower, narrower, longer, and 

 reaching to their tip. At first glance these specimens have a less 

 hirsute appearance than those of C. atrox. In accordance with the 

 narrowness and the smaller number of their scales, their body ap- 

 pears more slender. 



I am well aware that the coloration does not afford safe specific 

 characters, except in comparatively few instances ; but as all the 

 specimens I referred to C. atrox agree so well in this respect, dif- 



