54 BULLETIN 199, XHSTITED STATES NATIONAL MUSEUM 



Range. — Extreme southwestern Canada and extreme southeastern 

 New York, southward throughout the Americas; Bermuda Islands; 

 West Indies; Revillagigedos Islands; Galapagos Islands; Madagascar 

 (two genera); Fiji and Tonga Islands (one genus). 



KEY TO MEXICAN GENERA OF IGUANIDAE 



1. No femoral pores 2 



Femoral pores present, conspicuous in males, less well defined in females. _ 5 



2. Ventral lamellae on next to last phalanx of digits expanded laterally, forming 



a padlike structure; posterior part of head not produced Anolls (p. 55) 



Ventral lamellae on digits not expanded to produce a pad; posterior part of 

 head more or less produced 3 



3. Infradigital lamellae with a single, tubercular keel Laemanctus (p. 69) 



Infradigital lamellae with several sharp keels 4 



4. Toes with a lateral fringe Basiliscus (p. 71) 



No fringe on toes Corythophanes (p. 68) 



5. A single, median, dorsal, longitudinal series of enlarged scales 6 



Scales in vertebral row not conspicuously if any larger than adjacent scales. 9 



6. Tail with whorls of much-enlarged, spiny scales, usually separated from each 



other by whorls of small scales 7 



Scales on dorsal and lateral surfaces of tail (except the vertebral row) subequal 

 in size, small 8 



7. A group of much enlarged, spinose, protuberant scales on shank and some- 



times on thigh; basal caudal region (or entire tail in short- tailed species) 

 highly modified, sometimes flattened and widened, with whorls of greatly 

 enlarged scales separated from each other by no more than 1 row of small 



scales; total length less than 450 mm Enyaliosaurus (p. 75) 



No conspicuously enlarged scales on shank or thigh; basal caudal area much 

 like rest of tail (which is always long), not flattened but cylindrical, with 

 whorls of enlarged scales separated from each other by two or more rows 

 of small scales throughout most of tail; total length often more than 450 

 mm., reaching at least 1,200 mm Ctenosaura (p. 73) 



8. A large, circular shield below tympanum; a well-developed gular append- 



age Iguana (p. 72) 



No shield below tympanum; no gular appendage Dipsosaurus (p. 77) 



9. Head bearing bony spines posteriorly, or elevated somewhat in a projecting 



ridge Phrynosoma (p. 94) 



Head normal, not i^roduced posteriorly in a bony ridge or in spines 10 



10. Superciliary scales not imbricate, but juxtaposed, like other scales on head; 



rostral subdivided, with a median suture meeting lip Sauromalus (p. 79) 



Superciliary scales strongly imbricate, large; rostral not divided, no median 

 suture reaching lip 11 



11. Sutures between supralabials diagonal, not vertical; mental very small, 



bordered posteriorly by a median postmental 12 



Sutures between supralabials vertical; mental larger, not bordered posteriorly 

 by median postmental 14 



12. No ear opening Holbrookia (p. 81) 



A distinct ear opening 13 



13. Interparietal much smaller than ear opening, not more than twice as large 



as any other dorsal head scale; several enlarged auricular lobules; a patch 

 of enlarged scales with projecting points on rear of femur Uma (p. 89) 



