""""I'syl!'' ] PUOCKEDINGS OF THE NATIONAL MUSEUM. 645 



Heterodon nasicus iiasicus I'M. aruldinl. 



Jh'terodoii nasicus lid. ;iml (iinl., C;il., I'l. i, Sorporils, Idf.:!, p. \\\. 

 Ifihrodon nimus nasicus Copi,', C!lu!ck Lint H;itr. licpt. N. AiiuT., IHTf). p. 4M. 

 Jiiii, Icon. ({on. Olid., Livr 10, PI. v, Fij^r. i. 



Central and Sonoran refjions. 



EUTJENIA li.l. :iii<l Oir.l. 



Cat. Serp. N. Anier., 1853, p. 24; Cope, I'roc. Anic-r. I'liilt.s. .><..(■.. l-sc, p. i;:,. 

 Thamnojyh is Fit'/,. Syst. Re))t., 1843, p. 26 (noinen miidinn). 

 /'>7/;HH07HJorfoH Cope, Proc. Acail. Pbila., 1860, p. 558. 



The genu.s EntuMiia presents especial attnictions to the student wlio 

 desires an illiistraUon of the i)hen()niena of variation and constancy in 

 the i>ii.ysical characters of animals. In few j;eneia do \vc find so well 

 illustrated the persistence of specilic characters exhibited side by side 

 with variations of the same. We have here, therefore, examples of the 

 appearance or disappearance as the case may he, of characters, in con 

 iiection with or without apparent connection with, the environment. 



This genus was established by liaird and (riraid in tlie Catalogue of 

 Ser[)ents of North America, pul>lished in 1.S53, on species winch had 

 been prevu)usly referred to the genus Natrix (Tropidonotus). To the 

 three species previously known, these authoi-s added four, and niin- 

 names were jn'oposed for what are in my estimation either sultspecies 

 or individuals of the seven species actually distinguished; in the year 

 1850 Kennicott added live species; at various dates between IStJOaud 

 1885 the present writer added nine species ami referred to the genus a 

 species long previously described by Wiegmann : in 181KI Hrown added 

 a s])ecies; arid a species is «lescribed for the lirst time in the present 

 review. The total inunber of si)ecies is then twenty-fbui". 



The characters of the genus are as follows : 



w!ubfamily Natricina'. Cephalic plates in)rmal : two nasals, one loreal. 

 l)late Eyer esting on superior labials. Scales keeled, without pits. Anal 

 |)late entire; subcaudais divided. 



The maxillary teeth are rather abruptly longer at the i)osterior e.x- 

 tremity of the maxillary bone than elsewiiere, as in thtigeiuus Natrix, 

 with two excei)tions. These are the species /v. multimttcuhttn Cope and 

 E. mchuuxjastcr ^\'iegm. I have on this account distinguisjied these 

 species as (tonstituling another genus which I called Atomarchus, the 

 (diaracter distinguishing it from EutaMua being tlie equality in lengtii 

 of the maxillary teeth. As the excess in lengtii of tiie posterior teetli 

 is small in some of tiie species of tlie latter, I lia\e not for the present 

 retained this genus, although it may be found to be advi.salde to d«> so 

 hereafter. 'I'he two species mentioned are nioi-e aipiati • in their liabits 

 than the EulaMiia' jjroper. 



lOutaMiia' are the most abundant snakes in Xorlli .Vnieri«-a and Mex- 

 ico. Where all other siundes are ab.sent, eitlier tliroiigii liostility of the 

 climate or of enemies, individuals of this genus remain. This persist- 



