DIADECTID^. 



101 



longer diameter ; alveoli not separated. Teeth on the vomer. No 

 secondary posterior nares. YertebraB notochordal, with intercentra ; 

 neural spines of moderate height, zygosphenal (hyposphenal) articu- 

 lations present, and the pre- and postzygapophyses approximated to 

 one another, with horizontal articular surfaces. A tusk may or may 

 not be present, and there may be either one or two rows of cheek- 

 teeth. 



This family has been regarded by its founder, Cope \ as repre- 

 senting a distinct subordinal group — Cotylosauria — on account of an 

 apparent peculiarity in the articulation of the cranium with the 

 vertebral column. Later on, however, it was suggested that this 

 peculiarity might be due to the loss of the basioccipital 2 ; and in a 

 subsequent memoir 3 this family is placed immediately after the 

 Bolosauridce, which apparently implies that its subordinal dis- 

 tinction had been withdrawn. 



Fig. 20. 



Empeclias molaris. — Oral and lateral aspects of a cheek-tooth ; from the 

 reputed Permian of Texas. \. 



Genus EMPEDIAS, Cope 4 . 

 Syn. JSmpedocles, Cope \ 



The dentition forming an uninterrupted series without a distinct 

 tusk, and the incisives only distinguished from the cheek-teeth by 

 their form, having more or less distinct transverse edges 6 . Number 

 of upper teeth varying from 1-4 to 16 ; cheek-teeth in a single row. 



1 Amer. Nat. vol. xiv. p. 304 (1880). 



2 Proc. Amer. Phil. Soc. vol. xix. p. 47 (1880). 



3 Trans. Amer. Phil. Soc. vol. xvi. p. 288 (1886). 



4 Proc. Amer. Phil. Soc. toI. xix. pi. v. (1881). This plate, although 

 referring to p. 56, was not issued till the next No. (108) in June 1881. 



5 Ibid. vol. xvii. p. 516 (1878).— Preoccupied by Stfil, 1867. 



6 See Cope, Amer. Nat. vol. xiv. p. 304 (1880). 



