1'hERIODONI S AND THEIR ALLIES. 29 1 



CLASSIFR'ATKJX. « 



While it is impossible in .lealiny with imperfect fossil remains 

 to tlo more in the \va\ of classification than approximate to the truth. 

 I advance the following scheme as the most satisfactory that can 

 be (lone in the present state of our knowledge. One or two ver\ 

 imperfectl) known forms which may Ije the types of new sub-orders, 

 or even of orders, have been omitted from consideration, as the 

 evidence is too slight to go upiu. I refer to such forms as Deljjhino- 

 gnathus. Tapinocephalus and Sclerosaurus. Most taxonomists 

 have placed the Placodontia with the Theriodonts — Seeley going 

 even further, and suggesting that they ma\ form a division of the 

 Deuterosauria. The order is. however, so imperfectly known that 

 it is probablv wiser to do. as has been done bv Lvdekker. leave it 

 to stand alone. There is certainK no satisfactory evidence for 

 placing it among the " Theromorjjha. its affinities being quite as 

 much, or probablv more, with the Sauropterygia. 



?.HV\('HO('ErHAI.OiD ORDERS. 



PKOCOLOPHOXIA. 



Lacertiform reptiles. Tem[)oral region roofed. Distinct post- 

 frontals. postorbitals. squamosals. su])ra-lemporals. and quadrato- 

 jugals. Palate Rhynchoce])halian in tv])e; teeth on pterygoids and 

 prevomers. Vertel)rae notochordal, with intercentra. Sacral \erte- 

 brae 4. Afxlominal ribs present. Scapula jilatedike. with no 

 acromion: no cleithrum. Humerus with entepicondvlar foramen; 

 phalangeal formula j. 3. 4. 5. 4. Pubis ami ischium platedike. [)ubis 

 pierced bv jnibic foramen, ilium short and broad. 



Familv : Procolophonidae. 



Genus: Procolophon. 



PELYCOSACRIA. 



Moderately large reptiles, with enormoush developed vertebral 

 si)ines. Tenijioral region with two arches. Distinct ]iostfrontals, 

 postorbitals. .squamosals. supra-temporals and quadrato-jugals. 

 Quadrate small. Palate a modification of the Rhynchocephalian 

 type; teeth on i)terygoids. palatines and prevomers. Vertebrae 

 notochordal. with intercentra. Abdominal ribs present (Thero- 

 l)leura). Scapula flat, with no acromion : no cleithrum. Humerus 

 with entepicondylar foramen. Pubis and ischium flattened, 

 divergent. 



Family : Clepsydropidae. 



Genera : Clepsydrops. 

 Dimetrodon. 

 Naosaurus. 

 Embolophorus. 



