30 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



color types, or subspecies, in an analytical key, in a 

 " Review of the Characters and Variations of the 

 Snakes of North America," I8Q2. 1 I have also given a 

 series of figures representing the North American color 

 forms, for which I am indebted to the United States 

 National Museum, which are here reproduced. 



Before going further into the patterns of the Osce- 

 ola doliata, I give a synoptic key of them. 



I. No yellow band posteriorly from orbit (a yellow half-collar). 

 a. Dorsal spots or saddles (red) open at the side, the borders of 

 adjacent spots forming pairs of black rings. 



Interspaces between red saddles open below ; scales not 

 black-tipped ; front more or less black ; first black ring 

 on nape only : O. d. cocdnea. 



Interspaces between red saddles closed by black spot be- 

 low ; scales black tipped ; front black ; first black ring 

 complete : O. d. polyzona. 



Interspaces not closed ; rings, including first, complete on 

 belly; first yellow band crossing occipital plates; front 

 black ; scales not black-tipped : O. d. coiijuncta. 



aa. Dorsal spots closed at the sides below, forming saddles. 

 b. Saddles closed by a single black tract on the middle of the 

 belly; no spots between the saddles. 



Dorsal spots undivided medially; front black ; first black 



ring complete : O. d. annulata. 



Dorsal spots divided longitudinally by a median black 



connection ; front black : O. d. gentilis. 



bb. Inferior borders of saddles separate and not confluent with 



each other. 



Saddles completed on gastrosteges ; no alternating spots ; 

 no black collar : O. d. parallela. 



Saddles completed on gastrosteges ; spots opposite inter- 

 vals forming a single series on the middle line of the 

 belly : O. d. syspila. 



Saddles completed above the gastrosteges ; alternating 

 spots which do not meet on the middle line of the belly: 



O. d. do Hat a, 



\Proceedingsofthe U. S. National Museum, XIV, p. 589-608. 



