CROCODILIANS, LIZARDS, AND SNAKES. 627 



Besides the family characters, this geuus is well distinguished among 

 American lizards by the divided frontal; the overrooting the temporal 

 fossa by the postfrontal and supratemporal; the descending process of 

 the j>arietal; forms of the xiphoid rods, and forms of the pelvic bones. 



In the latest enumeration of the species of this genus, that of 

 Boulenger, thirty-one species are included. These are distributed as 

 follows : 



North America 16 



Mexico 6 



Paleaarctic Region (North Africa) 1 



Paleaarctic Region (Asia) 7 



Southwest Asia. 1 



Total 31 



For purposes of analysis, the North American species may be 

 arranged in four groups, which have the following characters: 



A postnasal and one mental plate I 



A postnasal and two mental plates II 



No jjostnasal and two mental plates Ill 



No jjostuasal and one mental plate IV 



It may be also stated here that all the species have four supraorbital 

 plates except E. egregius, which has but three. Also that U. longirostris 

 ha^ more numerous scales than any other species, as they are in 30-34 

 rows: while in U. egregius the number of scale rows is smaller than in 

 any species, reaching only twenty-two. 



The form of the jjostnasal plate presents considerable variation in 

 some species. This is especially the case in E. muUivirg((tns, where it 

 may or may not reach the supranasal, and is sometimes directly under 

 the prefrenal. The opposite sides are sometimes slightly different. In 

 some species with two mentals they may be sometimes abnormally 

 fused together. 



All the North American skinks lose these distinctive marks of color 

 with age. All are dark, nearly black, when young, varied with white 

 lines or spots, which leave a trace of their presence when old. Three 

 of the labials, the upper especially, are black, with white centers. 

 There is always retained a dusky border to the lateral edges. If the 

 edge of the upper Jaw be white the character is never lost, the labials 

 never having darker lateral borders. The light lines in increasing age 

 generally remain for a time and are bordered by blackish or dark 

 brown, the interspaces generally becoming light olive. Even these, 

 however, gradually disappear, and the scales generally are olivaceous 

 above, with dusky borders, especially where origiiudly dark colored. 



The following arrangement may be considered as defining the species 

 with two une(iual postnasals by the color of the young: 



A. Upper labials plain whitish; ground color black above, bluish beneath; beneath 

 head white. 

 1. Five white lines, all on adjacent edges of scales, the middle bifurcating on the 

 head //_ quinqiielineultis. 



