VAKIATIONS OF GARTER-SNAKES. 127 



that thov are directly related. In this connection it should be 

 noted that apparently in every series of scales nidanogaster is more 

 reduced than ungust'irostris. In the south melanogaster comes in con- 

 tact with two very imperfectly known forms with which I believe 

 it also to be related; these are scalans and ^^/te/iaa:", which will next 

 be discussed. 



SCALAR IS a 



Description. — It is nearly always difficult to })roperly determine the 

 characters and affinities of forms which are known from but few locali- 

 ties, owing to the fact that geographic differences are seldom revealed. 

 This is particularh' true of the garter-snakes of southern Mexico and 

 Central America, a region from which a number of species have been 

 described, none of which are represented in American museums by 

 more than a few specimens. Of these forms scalaris is perhaps the 

 best known, but, although access has been had to the material in the 

 U. S. National Museum, Academy of Natural Sciences of Philadelphia, 

 and the Field Museum of Natural History, it has been possible to find 

 a total of but nineteen specimens, representing five localities. 



As known at present, the form may be described as follows: Lateral 

 stripe on the second and usually the adjacent edge or half of the third 

 rows. Eye small. Dorsal stripe principally confined to the median 

 row. Dorsal scale formula, 19-17, 19-17-15, 17-19-17, 17-19-17-15, 

 or 17-15; supralabials, 7, very rarely 8; infralabials, usually 9, occa- 

 sionally 8 or 10; oculars, 1-3 or 1-2; ventrals, 134 (female) to 151 

 (male); Subcaudals, 52 (female) to 76 (male). 



Ground color above brownish ash, olive brown, or dark chocolate 

 brown; the first row somewhat lighter. Stripes light ash to dull 

 orange yellow. In some specimens there are no lateral spots to be 

 observed on the scales, and in others there is a row of dark transverse 

 bars between the third and seventh rows, inclusive, which alternate 

 with a series of small spots on the eighth and ninth rows. In th(^ ma- 

 jority of specimens, however, there is on either side a single seri{\s of 

 large (one and one-half scales wide and one a])art) rectangular, trans- 

 verse, dark brown sj)()ts with dark edges, which extend from about the 

 middle of the third to the median row of scales. These s]iots are well 

 defined from the nape (where they are represented l)y a ])air of large 

 nuchal blotches) to the anus, are as distinct in the young of the single 

 brood examined as in the adults, and the spots of each sid(^ are only 

 separated by the dorsal stripe on the median row. Head above brown, 

 generally marked with dusky yellow. Postoculars and supralabials 

 dusky yellow. The plates in the latter series may not be margincMl 

 with darker. 



n Thamnophis scalaris Cope. Proc. Acad. Nat. Sci. Phila., 1886, p. 306. Includes 

 T. scaliger Jan. 



