CROCODILIANS, LIZARDS, AND SNAKES. 



1139 



CTIOTJ^H.IN JR. 



Only two genera of this subfamily are known. 



Head with nine uoimal shields Sistrurus Garnian. 



Head scalfd above Crofalus Linna-ns. 



In Sistrurus tlie hemipenis is finely ilounced as is Ancistrodon 

 adding this point of resemblance to the i)()Ssession of similar head- 

 shields. In Crotalus the organ is strongly calyculate, the lower rows 

 becoming flounces in C. basiliscus and G. conjluentus, but not in C. hor- 

 ridfis, G. (litris.sus, nor G. molossm. My statement that the spines 

 are not ossified in the G. durissu.s, is due to the fact that I examined a 

 specimen not fully grown, although it was not a very small one.' 



This subfamily is characteristically Nearctic. There is but one species 

 [Grolalns terrificuH) which is characteristically Neotropical, and there 

 are two other Ootali (C. luguhris and G. basil iseus) which may range 

 into the Neotropical. A Sistrurus {8. ravus) may overlap in the same 

 way. The greater number of species belong to the Sonoran region. 



The geographical distribution of the Crotalinie is exhibited as fol- 

 lows — the genus Ancistrodon is added in illustration: 



' The structure of the organ is represented on pi. xxxiii, fig. 11, Trans. Amer. Phil. 

 Soc., XVIII, 18U5. 



