Acanthodactylus. 39 



The probable derivation of A. houeti, the southernmost African 

 species, from the northern A. vulgaris is entirely in accordance with 

 the views I have expressed on the dispersal of the Lacertidse. 



I have stated above that the striation of the young of some of the 

 lizards of this genus is more primitive than that of any of the Lacerta. 

 This view is based on the number of white streaks on the neck, which 

 may be as high as ten in some A. vulgaris and A. jmrdalis (6 dorsal 

 and a pair of lateral on each side), and it is a suggestive fact, in this 

 connexion, that, on morphological grounds, A. vulgaris is considered 

 as, on the whole, the most generalized species of the genus (the young 

 of A. fristrami is still unknown), whilst in the most extreme species at 

 the other end of the series, A. scutellatus, the light streaks, if present, 

 are not more than 6 in number (4 dorsal and 2 lateral). 



The distinction of species in this genus is a matter of considerable 

 difficulty, owing to the great variability in nearly all the characters 

 which have hitherto been used for the purpose, and the solution of 

 the problem must for the present rest on the taste and judgment of 

 the systematist. In the following revision I have utilized a very large 

 material (over 700 specimens), and the results of long study, at 

 intervals, for 40 years. If I have erred in uniting too many forms 

 under one species, I cannot incur the reproach of increasing the 

 confusion by doing so, as subordinate categories have been freely 

 recognized under the term " variety." 



In making use of the following synopsis for the identification of 

 specimens, difficulty may arise as to the exact number of longitudinal 

 series of ventral plates. It is often perplexing to count these series, 

 owing to a gradual passage, on the sides of the body, of the plates into 

 the enlarged scales ; for this reason the numbers given by me are not 

 always in accordance with those of other authors. According to the 

 system followed throughout in this family, I reckon as ventral plates 

 such of the outer series, whatever their width, as are as long as those 

 of the other longitudinal series. It sometimes happens, however, that 

 in one or two transverse series there is one plate more on one side of 

 the body than on the other ; in such cases I have not reckoned the 

 extra plate. 



Si/nopsis of the Species. 



I. Three series of scales round the fingers and toes. 



A. Only one or two large supraoculars, the (primarily) first and fourth, 

 or first, second and fourth, usually broken up into numerous small 

 plates or granules (the first rarely into 2 or 3 plates only) ; suh- 

 ooular often bordering the mouth ; dorsal scales small ; ventral 



