54 THE ZOOLOGIST. 



uncommon, and one in my possession from a small village about 

 five miles distant (Worth) measures as much as 25*1 cm. This 

 individual, a male, is otherwise interesting as possessing a 

 distinctly-developed gular fold, a feature as a rule not marked 

 in L. agilis. According to Bedriaga, the gular fold is charac- 

 teristic of some Eussian forms of this species, a circumstance 

 which appears to countenance his supposition respecting its 

 affinity with L. viridis, these Eussian varieties being, as he 

 shows, the intermediate links. I see Steindachner (' Schlangen 

 &c. der Galapagosinseln'), speaking of Amblyrhynchus, says, 

 " Some large specimens have a sulcus gularis, others have 

 absolutely none." The young of L. agilis possess a marked 

 gular fold, which, in the same manner as that of some caudate 

 batrachians, loses its distinctness at the approach of maturity. 



During the growth of the individual the collar which at first, 

 like that of L. muralis, is even-edged, becomes denticulated. It 

 is to be observed, however, that immediately after desquamation, 

 or with males of a bright green colour, the edges of the otherwise 

 pigmented collar are often quite translucent, the green colour 

 exhibiting an even line, as though the collar were not serrated. 



It is open to question whether much stress should be laid on 

 cases of individual variability such as these, though they may 

 under circumstances give a clue to generic relationships. As 

 another example may be adduced the variability in the rows of 

 ventral plates of certain species, which has caused some difficulty 

 to systematic naturalists ; as also the irregularities occurring in 

 the plates on the head. From a considerable list of such 

 irregularities which I have tabulated,* it appears that (1) they 

 occur more frequently with the male than with the female; 

 ('2) some correlation appears to exist between certain plates, the 

 variability of one entailing that of another ; (3) some irregularities 

 are more liable to occur than others, and in an analogous manner 

 with different species of lizards. 



This tendency in different species to present analogous vari- 



* As: occipital rudimentary, often absent; internasal very variable in 

 shape and size ; between the latter and the frontonasalia a small plate often 

 inserted; interparietal divided into small plates; two plates joined together 

 without a division, or all plates irregular (perhaps the result of an external 

 injury), &c. 



