190 REPORT OF NATIONAL MUSEUM, 1898. 



I. Ceratohyal present. II. Ceratohyal absent. 



A. A second ceratobrauchial. 



Vertebral column. — Except in the families of the GeckonidiB and 

 Uroplatid.T, the vertebral centra are procnelous. In the families named 

 they are amphica?lons. The zygosphen articulation is present in the 

 Teiidae and the larger Iguanidse, including a rudiment in CrotaiJhytus. 

 In smaller Iguanidse {Sceloporus, Phrynosoma) and in Sauria generally 

 this kind of articulation is wanting. In a good many families the 

 caudal vertebra? are divided by a transverse fissure or suture in front 

 of the middle, which often splits the base and sometimes the length of 

 the diapophysis. Such a structure is seen in Iguanidai {lgi(ana, Sauro- 

 malus, Sceloporus, Dipsosaurus), Anolidai, Anguidse (Celestus), Teiidai 

 {Tupinamhis, Cnemidophorus), Lacertidae {Lacerta), and Scincidae 

 {Gongylus, Eumeces). In Dipsosaurus, Anolis, and Lacerta the neural 

 spines of the caudal vertebra? are double; in the other genera named, 

 single. In Varanidae, Helodermidse, Gerrhonotus, Grotaphytus, and 

 Phrynosoma, the caudal centra are undivided, and the neural spines 

 are single. In Ophisaurus the centra are undivided and the neural 

 spines double. The centra are excessively thin in Ophisaurus, so that 

 they break more readily than they disarticulate. There are two sacral 

 vertebra except in genera with the posterior limbs rudimental or 

 absent. In some of these, however, especially the degenerate genera 

 of the Anguida", the rudimental ilium is attached to two diapophyses 

 which join each other distally. 



Intercentra are present in the cervical and caudal regions in the 

 latter, supporting the chevron bones. Besides the intercentra there 



