%Uh'''j PKOrEEDINGS OF THE NATIoNAE MUSEUM. 639 



This <;enus of Colnbriiu! siiaki's includes mtlKT lar;;c ami lolmst spo- 

 cies. They are restricted exclusively to the Nearctic Jiealni and the 

 Lower Californian district of the Neotropical. Tiiey are entirely ter- 

 restrial in their habits, preferring dry and even sandy regions to any 

 other. They are of a harmless disposition as a general rule, Imt tlic /'. 

 fiayi hcUona defends itself vigorously when attacked. The peculiar 

 epiglottis, first observed and described by Dr. C. A. White of Wash- 

 ington, aids these snakes in emitting an unusually loud hiss on tlic cx- 

 l)iration of the air contained in their voluminous lung. This sound, 

 although it cannot be called a voice, is sutticiently loud to be alarming, 

 and serves no doubt as a defense. 



The question as to the number of species included in this geiuis is a 

 dillicult one to decide. The P. melanolcucii.s may be always distin- 

 guished by color characters from the forms found west of the Missis- 

 sii)pi KMver. From some of these it also dill'ers in the shape of tin' head 

 and iiuizzle, but the most eastern of the western forms, /*. .sai/i sat/i, 

 rt'sembles it in these respects. The Lower Californian form may be 

 distinguished from the /'. mclanoleiicus by color characters, and by the 

 shape of the head and muzzle, but between it and the P. .saj// of the 

 western Mississippi region there is a complete transition in most of the 

 characters. The California form resembles that of Lower California in 

 form, but (lifters iu color, while the Arizona form is in every resi)ect 

 internu'diate between the Pacific form (P. catcnifer)^ and th(» /'. sayi 

 of the plains. These forms are tolerably constant an«l can be generally 

 recognized. The form of the rostral plate is the most characteristic 

 ])eculiarity, but, from the nature of the (;ase, transitions occur. Under 

 the circumstances I have adopted four species, of which the P. saifi h.is 

 two subspecies, one of which, /', .s. hclloiia is intermediate between its 

 typical form and the 1\ eaten i/c r ; the latter <lilfering, liowever, in the 

 greater smoothness of the scales. 



SVNOPSrS OK SrKClKS. 



Sculi's with strniif^tT kcol.s ln'i^iiiiiinj^ on tlui fourlli row ; lieail Hliort, rU'vatril, ro.s- 

 tral plato coiiipresscd, and uarrowod abov»^ ; uo lusul slripoN; dorsal Npotn ft'w, 

 27-3:5 on body /'• tHelrtiiolcucuB. 



Scales first kcelod on the sixth row; rostral plato narrowml above ; lu-ad sfripoH 

 present; spots nniiierons, I ()-<;.') on liody I', ndi/i. 



Scales weakly keeled, first on tenth row; rostral little prominent, not narrowoil 



above; head llat ; head stripes present ; spot^s nnineroiis. ;U>-7'J on boily 



/'. rat) nifer. 



Scales weakly keeled, be;;inninf; on tenlii n>\v; rostral plati; not narrowed, and little 

 prominent; head tlat ; spots few, 40-41 on i)ody, anteriorly red; no lie;wl-stripe«. 



/'. rerteliralis. 



The head stri[)es consist of a band exteiuling from the eye to the 

 angle of the mouth, another fiom the eye to the upper lip below it, and 

 another across the lV(uit of the frontal plate <ronuectiiig the ori)its. 

 .These stripes are_ present iji the young of the species which lack them 



