AKT. 12 EEVISION OP LIZAEDS OP GENUS CTEFOSAURA — BAILET 6 



which some of the earlier described species of Ctenosaura were 

 assigned. The two genera are very closely related, but may be read- 

 ily distinguished from each other by a comparison of the soles of the 

 hind feet; in Cyclura there are peculiar corneous combs or pectina- 

 tions on the under side of the toes; the toes of Ctenosaura are with- 

 out such corneous combs. 



The species are powerful and very active, and can make a good 

 defense when necessary by the use of their small sharp teeth, and of 

 their spinose tail. This organ is armed with whorls of spinous scales 

 which are very acute and which inflict considerable wounds when 

 driven against the naked surface of the skin. Ctenosaurs are not 

 much valued as food by the natives of Mexico and Central America, 

 except by some Indians, and like other large tree and rock lizards 

 are called iguanas. 



We know very little if anything of the geologic history of this genus, 

 and one simply gropes in the dark in attempting to treat of this phase 

 of the subject. However, a few facts relative to the family Iguanidae, 

 to which this genus belongs, will be given merely to throw some light 

 on the possible origin and distribution of the group. All of the 

 Iguanidae are confined to North and South America with the excep- 

 tion of one genus {Brachylophus) which inhabits the Fiji Islands and 

 two others {Chalarodon and Hoplurus) living in Madagascar. A fossil 

 species of iguana {Iguana europaea) has been described from the 

 Eocene deposits of France and England. The Cretaceous genera 

 Iguanavus and Chamops from Wyoming have always been considered 

 as belonging to the Iguanidae, so there is no reason to doubt that the 

 family has originated in America and that it was present during the 

 latter part of the Mesozoic era. 



Although no very satisfactory conclusions, perhaps, can be reached 

 regarding the main question of the origin of the species of Ctenosaura, 

 the data derived from this study indicate very strongly the close 

 relationship to, and their origin from, a common iguanid stock. 

 Also from the present distribution of the species it seems but logical 

 to believe that they originated at some place in central western Mex- 

 ico, probably Nayarit and Jalisco, and that they have spread thence 

 northward and southward until they cover practically the whole of 

 Mexico and Central America. The transition in morphological char- 

 acters has been gradual, and there is no obvious break in the series, 

 indicating, of course, land migration only. 



By a strange coincidence the type, Ctenosaura acantJiura, is both 

 the most primitive and the most widely distributed species of the 

 genus, and evidently had, at an early date, firmly established itself 

 throughout Mexico, being numerous on both the east and west coasts. 

 Even to-day this species has practically the same distribution. 



