332 REPORT OF NATIONAL MUSEUM, 1898. 



The hemipeiiis is bifurcate, and lias a strong welt opposite to tlie 

 sulcus spermaticus. The surface of the organ including the welt is 

 covered with a rather close honeycomb structure without the interrup- 

 tions seen in the genera more nearly allied to Iguana, etc. 



Reproduction. — The males are generally more brilliantly colored, and 

 larger than the females. The latter are generally oviparous, but the 

 species 8. viviparus of the warmer parts of Mexico is viviparous. 



The species agree in possessing the following external characters: 

 Head, depressed, tetrahedral, rather broad ; behind the forehead, sloping. 

 Canthus rostralis continued nearly to the end of the snout; the nostrils 

 superior; plates on the top of head large, not many in number, and quite 

 symmetrically arranged. The supraorbital region, with one or two cen- 

 tral series of large transverse plates, bordered internally by one, exter- 

 nally by one or two series of small plates independently of the elongated, 

 angular ones forming the extreme edge of this region or jiart of the 

 canthus rostralis. There is a large occipital, with a smaller on either 

 side, sometimes with a line of two or three. Next comes two plates 

 between the orbit, sometimes with a smaller interposed, sometimes dis- 

 placed by the occipital. Next a vertical, followed by a second, which is 

 sometimes divided into two lateral. Then come two plates, then three, 

 then four to the nasal plates, with four between them. An additional 

 rostral median jilate is sometimes inserted, around which are grouped 

 four or five scales; this involves a difl'erent arrangement of the remain- 

 ing ones. The nostrils themselves are rounded and situated in the 

 center of a single nasal plate. 



There is no fold on the throat, the scales there being like those on 

 the breast. There is, however, an oblique fold of skin on each side the 

 neck covered with large scales and overlying a pit lined with fine gran- 

 ular scales*and usually harboring Acari. 



All the scales on the body are ovate, imbricate, and generally strongly 

 carinated, except below. The upper ones generally have a prominent 

 spine behind, and the edges are more or less denticulated, rarely even. 

 The scales of under surface are usually notched or emarginate between. 

 They are sometimes faintly carinated, with those on the inside of tibia. 

 The relative proportions of scales on different parts of the body varies 

 considerably Avith the species. 



The ears are distinct, usually with a serrated margin anteriorly. 

 There are eight to twenty femoral pores, but no anal ones. The male 

 has two or more large concave plates just behind the anus, which are 

 wanting in the female. 



The color varies with the species, though there is generally a light 

 lateral stripe (sometimes two) on each side. The back is marked with 

 transverse dark lines or with blotches. The males have a blue blotch 

 on the under surface and on the sides of belly. 



The species are rather numerous. Since Wiegmann described the 

 most abundant of the Mexican species, synopses have been published 



