VARIATIONS OF GARTER-SNAKES. 9 



there are frequently two, in two others (angustirostris and melanogas- 

 ter) mostly two, and in one (angustirostris) frequently three. 



The postoculars are most often tliree in number, occasionally 

 varying individually to two or four, in one form {melanogaster) being 

 very frequently two. The temporal plates are ordinarily one fol- 

 lowed by two or three, but in one form (hutleri) there is frequently 

 but a single plate in the second row; occasionally the first temporal 

 is divided, and frequently there are four scales in the second row, but 

 these are individual variations. The supralabials are 6, 7, 8, or 9 on 

 either side, the eye resting upon the third and fourth, or fourth and 

 fifth, except in angustirostris in which the lower postocular is pro- 

 longed forward beneath the eye to separate the orbit from all but 

 one supralabial. 



There is a triangular mental plate at the symphysis of the lower 

 jaw, and posteriorly from this the infralabial plates, 8, 9, 10, or 11 

 (very rarely 12) in number, extend to the posterior angle of the 

 mouth, being separated, except the first pair, which are prolonged 

 inwardly to meet on a median line, by two pair of chin shields. The 

 anterior })air of chin shields is usually the shorter, but in two forms 

 (ordinoides and elcgans) they are quite constantly equal or longer 

 than the posterior pair. 



The maxillary teeth are apparently as in the other forms in the 

 family, i. e., rather abruptly longer near the posterior end of the 

 maxillary bone than anteriorly. The genus Atomarchus Cope (Sti/po- 

 cemus, CJiiloponia) was based on forms in which the maxillary teeth 

 were equal throughout (melanogaster and angustirostris), but, as 

 later stated by Cope, the excess in the length of the posterior teeth 

 is so small in many specimens of other species that it is impossible 

 to distinguish them from apparently isodont specimens of these 

 i'orms, wliile we have, moreover, seen specimens of melanogaster in 

 which the posterior teeth were nearly, if not quite, as elongated as in 

 an}' form in the genus. 



On the body there are 17 to 23 longitudinal rows of dorsal scales; 

 these being normally arranged in an even number of rows on either 

 side of a mechan dorsal s(>ries. The scales are all keeled with the 

 exception of those of the first row, which are usually smooth or but 

 weakly keeled; in one instance (melanogaster) those of the second 

 row also tend to become smooth, the keels being generally weaker 

 than those of the rows above. 



The abdominal j)lates consist of a single series of large transverse 

 scutes that vary in numlxM" both individually and racially, the ex- 

 tremes for the genus being about 132 to 180 from chin to anus. 

 The anal plate is almost invariably entire, while the subcaudal 

 plates, wliich like the abdominal plates are also variable in num- 



