BATRACIIIANS AND KI':PTILP:S, CENTRAL AMERICA AND MEXICO. 61 



II. Gastrosteges ^vide, witli two keels. 



Scales imbricate ; one nasal Aepysurus Lacep. 



Top of head scaly ; two nasals Pelagophis Pet. & Dor. 



III. Gastrosteges narrow, rudimentary, or absent. 

 * Nasals separated by frontals. 



Gastrosteges distinct to vent IHstira Lacep. 



** Nasals contiguous. 



Head covered with scales behind.- Acahjptus D. A: B. 



Head short, entirely shielded : no syinphyseal notch Hijdropliia Daud^ 



Head moderate, entirely shielded; a deep symphyseal notch liiihydrina Gray. 



Snout long, spatulate Pelamia Daud. 



Najid^. 



I. Grooved teeth behind two jierforated teeth on the os maxillare. 

 Head-shields normal ; no loreal ; scales smooth ; form fusiform Ogmodon^ Pet. 



II. Solid teeth behind the fang on the os maxillare. 

 A. Loreal plate present. 



Subcaudals entire ; scales smooth Deimonia Krefft. 



AA. Loreal plate absent. 



a. The neck with few scales, not extensible. 

 [i. Subcaudal scuta one-rowed. 

 y. Scales of vertebral row equal to others. 



Nasals two ; scales smooth ; anal bifid Pseudcihis Wagl. 



One nasal ; scales smooth ; anal single Hophtceiihaliia'^CnY. 



One nasal ; scales keeled ; anal single Tropedechis Gthr. 



atx. Scales of vertebral line enlarged. 



Scales smooth ; two nasals; anal entire Z)««<7«rHs Daud. 



)iii. Subcaudal scuta two-rpwed. 

 y. Scales of vertebral row equal. 



Rostral plate normal; two nasals Diemen'ui' Gray. 



Rostral plate narrow ; produced backwards above ; two nasals Pscudonaja Gthr. 



Rostral wide, prominent, depressed ; one nasal Far inn* D. «fe B. 



Rostral normal; one nasal; anal double • Cacophia^ Gthr. 



■yy. Scales of vertebral line enlarged. 



Scales smooth Megcerophis'^ Gray. 



aa. Neck extensible, covered with more numerous scales. 

 fi. Anal entire ; subcaudals two-rowed. 



No postparietal plates Najiv Laur. 



Postparietals present OpUophaguH Gthr. 



III. No solid maxillary teeth. 



a. Subcaudal scuta iu two rows. 

 /?. Rostral plate much developed. 



Rostral free at the sides ; scales keeled Cyrtophis Sund_ 



Rostral not free; scales smooth ; anal entire A-spiddups Fitz. 



Rostral not free ; anal entire ; two nasals Ehinelaps Gthr. 



ii3/3. Rostral not enlarged. 



Scah^s keeled Sepedon Merr. 



Scales smooth Callophis Gr. 



aa. Subcaudal scutella iu one row. 

 One nasal ; a spine at end of tail Acanthophis Daud. 



' Labionaris Brocclii. 



^Alcctu Wagl. 



^Pseudoelaps T). &!&. Ula'pnoidea Bocage. HemibzuigarusVet. -, incladoa Brachysoma triste Gthr, 



* Brachyxirnj^hiti Gthr. 



^Jiraclnjaoma Gthr. Boulengerina DoUo. 



^ Xcnurelavs Gthr. 



' Tomyris Eichw. 



