ON CEETAIX ORXITIIOSAUEIA^^ AND DIXOSAURIAN EEMAI.XS. 41 



4. Oa certain Ornithosauriax and Dixosaurian Remains. 

 By E. Ltdekker, Esq., B.A., F.G.S. (Kead December 10, 1890.) 



[Plate V.] 



I MAY state, by way of introduction, that I am indebted to my 

 friend Professor 0. C. ^larsh for the correct determination of the 

 interesting- reptilian bones forming the subject of the present com- 

 munication. 



I. Ornitliosaurian Quadrates. 



When engaged in compiling Part I. of the ' British Museum 

 Catalogue of Fossil Eeptilia and Amphibia,' I was considerably 

 puzzled with three imperfect bones from the Ivimeridge Clay of 

 Weymouth, Eventually I considered that they represented a 

 peculiarly modified ulnar metacarpal of an Ornithosaurian ; and 

 they were accordingly entered at page 41 of the volume cited 

 (Xos. 43034, 44183, and 41179) as the distal extremities of that 

 bone. It was mentioned at page 40 of the same volume that these 

 bones differed from normal specimens of the ulnar metacarpal in 

 having a flat bony plate attached to one of their lateral surfaces, 

 which I considered might have aided in the support of the pa- 

 tagium. 



The resemblance of the free trochlear extremity of these bones to 

 that of the distal extremity of the ulnar metacarpal of an Ornitho- 

 saurian is, indeed, very striking ; but, on seeing them. Professor 

 Marsh at once said that the}- were Ornithosaurian quadrates. On 

 comparison with the quadrate of the skeleton of RJiampliorhynchus 

 Cuvieri preserved in the Museum*, and also with that of Sca- 

 pJiognatlms Purdonif (acquired by the Museum since the first part 

 of the ' Catalogue ' was written), no possible doubt remained as to 

 the correctness of this identification. 



In Plate Y. figs. 3 a, 3 6, 4 a, 4 h, views are given of two of these 

 Ornithosaurian quadrates, one (J^o. 44183) belonging to a small, 

 and the other (No. 41179) to a large form. Erom a comparison of 

 these specimens with the quadrates of SjyJienodon., HhampJwrhj/nchus 

 (/randis, and ScapJioj/nat/ms Pardoni. it is quite evident that they 

 belong to the right side of the skull. The distal extremity of each 

 forms a deeply-grooved oblique trochlea, above which there is a 

 nearly quadrangular shaft. To the inner side of this shaft is 

 attached by suture a flattened plate of bone, concave internally and 

 convex externall}', which, from the analogy of Splienodon^ must evi- 

 dently represent part of the pterygoid. In the larger specimen part 

 of tlie anterior free border of the pterygoid is preserved in the upper 

 part of the bone. To the outer surface of the distal trochlea of 



* Catalogue, &c., p. 33. no. 37002. 



t Phil. Tran8. for 1888, pp. 503-537, pis. Ixxvii, Ixxviii. 



