788 REPORT OF NATIONAL MUSEUM, 1898. 



the anterior. That this distinction is valid in many instances is well 

 known, but it is admitted by Boulenger that in otber instances the 

 transitions are complete. An examination of the penial characters 

 leads me to the opinion that each of these groups is a series of genera 

 rather than a single genus. Thus in the Zamenis gemonen.sis, the type 

 of the genus, we have the normal colubrine structure, from which two 

 divergent lines may be traced. In one of these, represented by the Z. 

 ventrimaculatus, the calyces preserve their character, but the lew papilLp 

 are ossified as acute siMnes, the character defining the genus Acantho- 

 calyx. In another direction the walls of the calyces are thickened and 

 support several series of papillte. This is seen in the Z. rarergierU. 

 In the next type these numerous papillae are ossified, giving us the 

 genus Gonyosoma. A greater modification is seen in the Z.JJorulentus. 

 Here the thickening of a part of the calyx walls is greatly increased, 

 while other walls, including all of the longitudinal ones, disappear. 

 The result is a mass of papillose pads, a character quite different from 

 anything else in the order and one which defines the genus Tylanthera. 

 The explanation of this structure is rendered possible by that of the 

 Zamenis ravergierii. 



The North American species referred to Zamenis by Boulenger have 

 been separated under the name Bascaniuni by Baird and Girard. 

 Most if not all of these species differ from the typical Zamenis gemo- 

 nensis in possessing one or two large hooks at the proximal ])art of the 

 spinous tract, which remind one of the Natricinie, and which are not 

 found in the typical forms of Zamenis. The Drymobiiis jmlcherrimus 

 Cope possesses a similar peculiarity, which separates it from the 

 typical species of that genus. It differs from the species of Bascaniuni, 

 however, in having the large spines distad to the spinous tract and_ 

 not proximad. 



The proposition of Boulenger to combine the forms into the genus 

 Zamenis, which have been hitherto separated, throws light on tlie sub- 

 ject, by emphasizing the weakness of the dental characters regarded by 

 Dumeril and Bibron as definitive of the genera so included. My dis- 

 covery of the penial characters, however, shows that this aggregate 

 includes several genera, which may now be satisfactorily defined. 

 Without these Boulenger's Zamenis is as difiicult to define as a whole as 

 any of the whole groups which he has included in it. How far some 

 of these penial characters are definitive of genera remains in some 

 cases to be ascertained. Thus the disposition of the large spines in the 

 American species is constant in all of them excepting in the Z. con- 

 strictor, where it is not constant; but I have not yet ascertained how 

 far this inconstancy goes, or whether it precludes the ultimate adop- 

 tion of the genus Bascanium or not. The definition of this group is as 

 follows : 



Head distinct; cephalic plates normal. Teeth increasing gradually 

 in size posteriorly, not grooved. Scales smooth, in an odd number of 



