ORDER ANOMODONTIA. 



I065 



Endothiodon has been compared to the Rhynchocephalian Rhy?icho- 

 sauridce and also to Placodus ; but although there is a marked super- 

 ficial resemblance between the three forms in the palate and teeth, 

 yet this resemblance is but apparent, since while in Endothiodon the 

 teeth are borne on a secondary bony floor beneath the narial passage, 

 in the other genera they are supported on the proper surface of the 

 palate, on which the posterior nares open directly, without the inter- 

 vention of a secondary passage. 



Suborder 4. Procolophonia. — According to a recent observer 

 the genus Procolophon, represented by comparatively small forms 

 from the Karoo system of the Cape, differs so decidedly from the 

 Theriodontia that it is entitled to form a distinct suborder, showing 

 marked signs of affinity with the Rhynchocephalia. The Procolo- 

 pho?iidce have a full dentition, but no tusk-like teeth, and the nares 

 are double. Although the pectoral girdle still has a distinct pre- 

 coracoid, yet its whole characters approximate to those of the 

 Rhynchocephalian genus Sphenodon. The humerus also resembles 

 the corresponding bone of the latter ; and in the skull the pterygoids 

 extend forwards in the same manner to join the vomers and exclude 

 the palatines from the middle line ; while there are no secondary pos- 

 terior nares ; and teeth are borne on both the pterygoids and vomers, 

 as in the young of Sphenodon. 



Group Placodontia. — Our sole knowledge of this group, repre- 

 sented by Placodus (fig. 986) and Cyamodus of the Middle Trias, or 

 Muschelkalk of Germany, is derived from the skull, so that we are 

 at present to a great extent in the dark 

 as to their true affinities. These forms, 

 after having been regarded as Ganoid 

 Fishes, were referred by Sir R. Owen to 

 the Sauropterygia ; and the type genus 

 resembles the Nothosaurs in the back- 

 ward position of the nares and the form 

 of the cranial rostrum. The skull has, 

 indeed, been said to present many points 

 of resemblance to that of the Anomo- 

 donts, and more especially Endothiodon, 

 to which genus it is considered by Sir 

 R. Owen to be closely allied. The re- 

 semblance in the form of the palate is, 

 however, as already mentioned, only a 

 superficial one ; the present form having 

 no floor to the narial passage, and the pos- 

 terior nares opening directly into the roof of the mouth by horizontal 

 apertures, as in the Sauropterygia. The skull is broad posteriorly, 

 with double nares, a deep and apparently compound temporal 



Fig. 986.— The imperfect palate 

 of Placodus gigas ; from the Mus- 

 chelkalk of Bayreuth. One-fourth 

 natural size. When entire the muzzle 

 would form a produced rostrum. 



