134 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



INTRODUCTION 

 Prefatory Remarks 



In two previous papers by the senior author the Snakes and 

 the Geckos of the Galapagos Archipelago have been studied, 

 and an attempt has been made to trace the history of these 

 islands from the evidence afforded by these two groups of their 

 reptilian inhabitants. It is now proposed to publish the re- 

 sults of a similar investigation of the lizards of the genus 

 Tropidurus — an investigation undertaken for the purpose of 

 confirming or disproving the conclusions reached through 

 study of the Snakes and Geckos. 



The material upon which this paper is based consists of 

 more than two thousand specimens from twenty-four islands. 

 The study of this collection has been an enormous task. Many 

 of the differences between species are differences in the size 

 and number of the scales. To show as clearly as possible all 

 differentiation along these lines, the scales around the middle 

 of the body, along the back, and along the belly have been 

 counted in fifteen hundred specimens, and the counts have 

 been charted island by island. This has involved the counting 

 of more than a quarter of a million scales. These counts have 

 all been made by Mr. Slevin in the following manner: 1. 

 Scale-rows — The number of rows of scales around the body 

 counted about midway between the fore and the hind limbs. 



2. Crest — The number of scales in the crest-row from the 

 point where the crest begins back to a line drawn across the 

 back at the level of the anterior surfaces of the thighs, the 

 thighs being held at right angles to the main axis of the body. 



3. Belly — The scales in a row along the middle of the belly 

 are counted from a line joining the anterior surfaces of the 

 arms when the fore limbs are held at right angles to the main 

 axis of the body, back to the anus. All measurements given 

 are in millimeters. All specimens are in the collection of the 

 Academy, and the numbers attached to them refer to the cata- 

 logue of specimens of the Department of Herpetology. Field 

 notes and descriptions of the coloration of living specimens are 

 in part by Mr. Slevin, and in part are quoted from Heller's 

 paper on the reptiles of the archipelago. While the specimens 

 are recorded as males and females, this determination of sex 



