LIZARDS. 25 



occasionally most of the bells (perhaps when worn out) drop off, and 

 a new set is developed. Rattles with a dozen or more bells are very 

 rare, especially at the present clay. No indication of a Snake's age 

 can be drawn from the number of bells in the rattle. Most Rattle- 

 Snakes have numerous small scales on the head and are included in 

 Crotalus, but in one species, constituting the genus Sistrurus, there 

 are nine large shields on the top of the head. 



Specimens of the ordinary North American Rattle-Snake 

 (Crotalus horridus, 325) and of a much larger South American 

 species (G. conflumtm, 323) are exhibited. 



Sub-order II. — Lacertilia. — Lizards. 

 (Cases 18-20.) 



The first representatives of the sub-order Lacertilia (of which Case 18. 

 the characteristics will be found on page 13) are the Geckos, con- 

 stituting the families GecJconidce, Eublepharidce, and Uroplatidce. 

 These reptiles take their name from the cry, " Geck-ko," of the 

 common Turkish species. The members of the typical family are 

 four-footed lizards, without movable eyelids, and with a broad fleshy 



Pig. 23. Fig. 24. 



Head of Indian Gecko (Gecko verticil- Hind-leg of Indian Gecko, from 

 latus), to show form of eye. the lower surface, to show the 



adhesive pads formed by parallel 

 transverse plates. 



tongue, slightly notched at the tip, and capable of being protruded 

 from the lips. The dentition is of the pleurodont type, that is to 

 say, the teeth are attached to the inner side of the outer parapet of 



