GECKONID^. 



posteriorly by a bony arcb ; thp postfronto-squamosal arch is like- 

 wise absent ; the pterygoids are widely separated and devoid of 

 teeth ; a columella cranii is present. The mandible contains only 

 five bones, the angular and articular having coalesced ; the dentition 

 belongs to the pleurodont type ; the teeth are small, niimerous, 

 closely set, with long, slender, cylindrical shaft and obtuse point ; 

 tho new teeth hollow out the base of the old ones. Only in a few 

 instances does the derm of the head coalesce with the skull, and a 

 supraorbital bone is present only in a few species of Tarentola. 

 Both pairs of limbs are constantly well developed and pentadactyle. 

 The clavicle is dilated, and perforated proxiinally; and the inter- 

 clavicle is subrhomboidal or of a shape intermediate between that and 

 the cruciform. The vertebrae are biconcave ; the ribs are long, and so 

 prolonged as to form more or less ossified hoops across the whole of 

 the abdominal region . 



The digits vary considerably, /and afford excellent characters for 

 systematic arrangement. Some Geckos (living in barren regions) 

 have the digits similar to those of many Agamoids, i. e. they are 

 subcylindrical or feebly depressed, and frequently keeled inferiorly 

 or denticulated laterally ; other forms with non-dilated digits have 

 them angularly bent at the articulations and provided with strong 

 claws ; but the greater number have the whole or part of the digits 

 dilated into adhesive organs with symmetrical plates or lamellae in- 

 feriorly, the arrangement of which varies considerably. Then also 

 the claw may be retractile, either between some of the lamellae oj 

 into a special sheath. Membranes may unite the digits, but the 

 web serves only for the purpose of obtaining a greater adhesive 

 surface, and never for swimming, none of the Geckos entering the 

 water. 



The body is generally more or less depressed, and may be bordered 

 by cutaneous expansions, the object of which appears to be, in most 

 cases, the same as that of the interdigital membrane ; but in the 

 curious genus Ptyehozoon, in which the lateral membranes attain 

 the greatest development, they act as a parachute. The tail presents 

 almost every possible shape, from the leaf-like tail of Oymmdae- 

 tylus platurus and the grotesque rudimentary tail of NepJirurus to 

 the slender rat-like tail of Agamura and the compressed crested 

 tail of Pristurus. This organ is, except in Agamura, ■ extremely 

 fragile and rapidly reproduced, in which case, however, it generally 

 assumes an abnormal shape and lepidosis. In some forms the tail 

 proves to be prehensile, a faculty which is possessed by few Lizards 

 other than the Chameleons ; and I am induced to believe that a 

 careful examination of the Geckos, when alive, will show this 

 character to be not unfrequent. 



The eye is generally large and with vertical pupil, which, when 

 strongly contracted, is frequently denticulated or assumes the shape 

 of two superposed rhombs ; some diurnal forms have the eye smaller 

 and the pupil circular. The eye is exposed, as in Snakes, covered 

 by a transparent lid under which it moves freeh', the valvular lids 

 being rudimentary ; in JEIurosaunts, however, there are connivent 



