Tliecodontosaurus and Palajosauriis. 145 



vol. V. pi. xxix. figs. 1 and 2), Paheosaurus cylindrodon {I.e. 

 fig. 4), and Pala'osaunts plat//odon (A c. fig. .0). The separa- 

 tion of these genera has not been unitormly adopted, though 

 they aj)pear to havti been founded Uj)on good characters. In 

 Thecodontosnurus the serrations upon the cutting-margins of 

 the teeth are inclined obliquely upward, somewhat like the 

 condition in Dimodosauru^. In Palceosaurus the corre- 

 sponding serrations are at right angles to the cutting-margin 

 of the tooth, as in Met/alosaurus. Therefore the dental 

 characters suggest a possible reference of the fixssils to distinct 

 families. But the nature of the serration has not always 

 been accurately represented, since in the British Museum 

 Catalogue of Fossil Reptiles, part i. p. 174, fig. 3, the lateral 

 serrations on the tooth of Palffosaurus j)latyodon are shown as 

 though they were directed obliquely upward ; and, in harmony 

 with this figure, tiie species is referred to the genus Tlieco- 

 dontosaurus. 



Messrs. lliley and Stutchbury made no attempt to divide 

 the bones which they found between their two genera. 



Sir 11. Owen, in 1841-42, in the Report of the British 

 Association, recognized a resemblance between the teeth of 

 T'hecodontosaurus, which he describes correctly, and the teeth 

 of Iihopalodon of Fischer, whicli are serrated in a different 

 way *, though there may be no implication that the serrations 

 are identical, since, while Thecoduntosaurus is said to have 

 the serrations directed vertically upward, the tooth-crown in 

 Palaosaurus is said to be traversed by " two opposite finely 

 serrated ridges, as in Tliecodontosaurus and Rhopalodon.^^ 



The authors who first made these animals known described, 

 in addition to teeth and jaw, vertebra3, ribs, chevron-bone, 

 and bones which were regarded as coracoid, humerus, radius, 

 ischium, femur, tibia, fibula, metatarsal or metacarpal bones, 

 and claw-phalanges. !Sir K. Owen [1. c.) grouped the more 

 important bones under the genus Tahrosaurus. He recog- 

 nizes resemblances in the vertebne to Teleosaurus and 

 UhijuchosauruSj in the humerus to li/ii/nc/wsaurus, and in the 

 femur to Crocodiles and Megalosaurus. The tooth in both 

 genera is regarded as Lacertian in form, and Thecodont in 

 implantation. The pectoral and probably the pelvic arch 

 are regard(;d as Lacertian. The double-headed ribs and 

 other vertebral characters, and the proportions of the limbs, 

 are interpreted as Crocodilian. 



These animals were afterwards referred to a distinct order 

 under the name Theeodontia ; and wiien they were redescribed 

 in Sir K. Owen's * Pala3ontology,' ed. 2, 1861, p. 275, the 

 * [Trans. Roy. Soc. vol, B cvi. 1894, pi. Ixiii. Hg. '2~\ 



