Thecodontosauvus and Palfeosauras. 145 



vol. V, pi. xxix. figs. 1 and 2), Palceosaurus cylinclrodon {I. c. 

 fig. 4), and Palceosaurus plaii/odoa {l. c. fig. 5). The separa- 

 tion of these genera has not been uniformly adopted, though 

 they appear to have been founded upon good characters. In 

 Thecodontosauvus the serrations upon the cutting- margins of 

 the teeth are inclined obliquely upward, somewhat like the 

 condition in Dimodosaurus. [n Palceosaurus the corre- 

 sponding serrations are at right angles to the cutting-margin 

 of the tooth, as in Megalosaurus. Therefore the dental 

 characters suggest a possible reference of the fossils 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 Palceosaurus platyodon are shown as 

 though they were directed obliquely upward ; and, in harmony 

 with this figure, the species is referred to the genus Theco- 

 dontosauvus. 



Messrs. Riley and Stutchbury made no attempt to divide 

 the bones which they found between their two genera. 



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

 Association, recognized a resemblance between the teeth of 

 Thecodontosauvus^ which he describes correctly, and the teeth 

 of Bhopalodon of Fischer, which are serrated in a different 

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

 are identical, since, while Thecodontosauvus is said to have 

 the serrations directed vertically upward, the tooth-crown in 

 Palceosaurus is said to be traversed by " two opposite finely 

 serrated ridges, as in Thecodontosauvus and Rkopalodony 



The authors who first made these animals known described, 

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

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

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

 and claw-phalanges. Sir R. Owen (/. c.) grouped the more 

 important bones under the genus Palceosaurus. He recoo-- 

 nizes resemblances in the vertebrse to Teleosaurus and 

 Rhyncliosaurus, in the humerus to Rhynchosaurus, 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 regarded 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 Thecodontia ; and when they were redescribed 

 in Sir R. Owen's ' Palaeontology,' ed. 2, 1861, p. 275, the 

 * [Trans. Eoy. Soc. vol. B cvi. 1894, pi. Ixiii. tig. 2.] 



