120 MARINE EEPTILES OF THE OXPOED CLAT. 



Mursenosaurus leedsi, Seeley. 



[Plates III. & IV. ; Plate VI. fig. 6 ; text-figs. 44, 59, 62, 63.] 



1874. Murcenosaurus leedsi, Seeley, Quart. Journ. Geol. Soc. vol. sxx. p. 197, pi. xxi. 



1881. Plesiosaurus leedsi, Whidborne, Quart. Journ. Geol. Soc. vol. sxxvii. table facing p. 480. 



1888. Plesiosaurus pUcatus, Lydekker, Geol. Mag. [3] vol. v. p. 351. 



1889. Cimoliosaurus iMcatus, Lydekker, Catal. Foss. Rept. Brit. Mns. pt. ii. p. 234 (pars). 

 1895. Murcenosaurus 2?licatus, Andrews, Ann. Mag. Nat. Hist. [6] vol. xvd. p. 429 (pars). 



Ti/j3e Specimen. — An imperfect skeleton, including portions of the skull and mandible, 

 most of the vertebral column, ribs, portions of the pectoral and pelvic girdles, and the 

 fore and hind paddles (R. 2421, Leeds Coll. 25), described and figured by Seeley, 

 loc. cit. supra (see also Pis. III. & IV. ; text-figs. 44, 59, 62, 63). 



In 1889 Mr. Lydekker referred to this form as Cimoliosaunis plicatus, but subsequent 

 descriptions * of the material from which CimoUosaurus was defined by Leidy f show 

 that this generic name cannot be employed in the wide sense in which Lydekker J 

 used it. The trivial name |J/^cai(^<s was used by Phillips § for a Plesiosaur which is 

 undoubtedly a species of Miircenosanrus, and was regarded as identical Avith M. leedsi 

 by Lydekker || and the present writer ^ ; but since it is now found that several species 

 of the genus occur in the Oxford Clay, and it is not certain to which of these the 

 vertebrge described by Phillips belong, it seems best to reject his name altogether and 

 adopt Seeley's name, his being the first description founded on adequate material. 



This species does not appear to have reached the large size and massive proportions 

 attained by Murcenosaunis durohrivensis ; at least the fusion of the cervical and caudal 

 ribs and of the neural arches is complete in comparatively small individuals. It is, of 

 course, impossible to say that these had reached their limit of growth, but it is certain 

 that in the other species a much larger size was attained before these signs of 

 complete ossification appeared. The same is true of the ossification of the scapula. 



Unfortunately the pectoral and pelvic girdles are very imperfect in the type 

 specimen, so that the important characters of these parts cannot be observed, but must 

 be inferred from other specimens. The characters by which this species is distinguished 

 from the other species here recognized, \iz. M. durohrivensis and M. platyclis, are : — 

 (1) The relatively small size of individuals in which ossification seems to be 



* Williston, '• jSTorth American Plesiosaurs : Elasmosaurus, Cimdliasaurus, and Pohjcoiylm,'' Amer. Journ. 

 Sci. [4] vol. xxi. (1906) p. 221. 



t Leidy, Proc. Acad. Nat. Sci. Philad. 18.51, p. 325 (1852). 



t Lydekker, Catal. Poss. Eept. Brit. Mus. pt. ii. (18S9) p. 180. 



§ Phillips, Greology of Oxford, etc. (1871) p. 313. 



II Lydekker, loc. cit. svpra. 



% Andrews, " The Pectoral and Pelvic Girdles of Murcenosaurus plicatv^," Ann. Mag. Nat. Hist. [6] 

 vol. xvi. (1895) p. 429. 



