62 MAEINE EEPTILES OF THE OXFORD CLAT. 



of its upper portion are strong rugosities for the insertion of muscles. The distal 

 expansion, which is mainly postaxial, is rather more distinctly marked off from the 

 shaft than in Pliosaurus. The general form and arrangement of the tibia, fibula, and 

 the other paddle-bones will be best understood from the figure. The tibia is the 

 largest of the other bones of the paddle ; it is rather longer than wide. Proximally 

 it articulates with the femur by a nearly straight surface ; its outer border is gently 

 convex, the inner (fibular) border concave. Distally it bears a long straight facet for 

 the tibiale and a short oblique one for the intermedium. The fibula also unites with 

 femur by a nearly straight border ; its postaxial surface is strongly convex, its anterior 

 (tibial) edge concave ; distally it bears facets for the intermedium and fibulare, making 

 a very obtuse angle with one another. The expansion of the femur extends con- 

 siderably behind the fibula and was fringed with cartilage, which may have enclosed a 

 posterior accessory ossicle, though no specimen has been found in which this is 

 preserved. 



The form and arrangement of the tarsals and metatarsals is the same as in other 

 members of the group, the fifth metatarsal as usual articulating directly with the 

 fibulare. The metatarsals are flattened and constricted in the middle. The phalanges 

 are likewise much constricted in the middle and are oval in section ; the number in 

 each digit is not known. 



Peloneustes philarchus, Seeley, sp. 



[Plate IV.; text-figs. 11-27.] 



1869. Plesiosaurus philarchus, Seeley, Index to the Fossil Remains o£ Aves, etc., in the Woodwardian 

 Museum, Cambridge, p. 139. 



1888. Tliaumatosaurus philarchus, Lydekker, Geol. Mag. [3] vol. v. p. 353. 



1889. P eloneustes philarchus, Lydekker, Quart. Journ. Geol. Soc. vol. xlv. p. 49. 



Type Specimen. — A considerable portion of a skeleton including the mandible and 

 part of the skull, from the Oxford Clay, Peterborough ; Porter Collection, Sedgwick 

 Museum, Cambridge. 



This species, founded by Seeley on the above-mentioned specimen, was never 

 adequately described by him and no figures were published. Subsequently it was 

 tentatively referred by Lydekker to Tliaumatosaurus, but the same author in describing 

 a considerable part of a skeleton of this species from the Oxford Clay of Kempston near 

 Bedford, collected by Mr. Crick (see p. 70), established the genus Peloneustes for its 

 reception. Subsequently he also referred Pliosaurus evansi, of the Oxford Clay, and 

 Pliosaurus aegualis to that genus. 



In this species the mandibular symphysis bears fourteen or fifteen teeth on either 

 side, and widens out very distinctly in the middle (text-fig. 27, A). These characters 

 distinguish it from the mandible referred to P. evansi, in which there are only twelve 



