Dinosaur from the Lower Lias. 575 



straight ; its height is about equal to its breadth. The 

 border of the articular face forms a sharp edge, behind which 

 the ceutrum contracts very rapidh^ in diameter; beneath 

 the pedicle of the arch the sides of the centrum are excavated 

 by a fairly deep elongated fossa. The anterior zygapopliyses 

 {a.z.^ are small, and project very little in front of the 

 anterior face of the centrum, their articular faces look 

 directly upwards. The diapophysis (d.p.), which is only 

 partly preserved on one side, projects upwards, making an 

 angle of about 45 degrees with the vertical plane. The 

 postero-ventral face of the diapophysis seems to have been 

 concave. There may have been a small parapophysial facet. 



The enlargemeut of the anterior lobe of the ilium sharply 

 differentiates this Dinosaur from the Triassic Theropods. 

 This expansion seems to be the consequence of the necessity 

 for a larger surface for the attachment of tlie ilio-femoralis 

 externus muscle, the enlargement of which, as von Hueue 

 has pointed out, is probably due to the adoption of an 

 upright bipedal mode of progression. This muscle is 

 inserted distally upon the great trochanter of the femur, 

 but, although this is better developed than in the Triassic 

 forms, it does not form the prominent flange of bone usual 

 in most of the later types ^, but remains small and peg-like ; 

 in this respect the present species occupies an intermediate 

 position between the Triassic and later Jurassic forms, such 

 as might have been expected from the horizon at which it 

 occurs. The development of the anterior pi"ocess of the 

 astragalus deduced by Dr. Smith Woodward from the 

 structure of the tibia, described by him and referred to above, 

 is no doubt correlated with the change iu the mode of 

 progression. 



The relatively large size of the pubes and probably of the 

 ischia seems to be a primitive character. 



The Dinosaurian remains above described certainly belong 

 to a member of the Megalosauridpe, but at the same tin>e 

 differ so considerably from the corresponding bones of 

 Megalosaurus itself that it seems necessary to refer the 

 species to a new genus, for which the name Sarcosaurus is 

 suggested, the specific name being Sarcosaurus ivoodi, iu 

 honour of the discoverer, Mr. S. L. Wood. Probably the 

 tibia described by Dr. Smith Woodward is referable to the 

 same species. 



* In Ceratosaurus the trochanter appears to have been considerably 

 smaller than in Anthrodemus (Alloaaiirus) or Megalosaurus, but, never- 

 theless, is larger than iu the present species. 



