Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/850

 two outermost of the three bones articulate with the middle one. One of these bones lies preaxially ; the other two are postaxial, the hindmost corresponding to the wing of the femur.

The preaxial bone (f) is pentahedral. It has a long proximal border, articulating closely (all the joints here are close-fitting) with the preaxial facet of the femur, and a rather shorter distal or tarsal border. Its mesial border, articulating with the middle bone, is shorter still. Its preaxial border, nearly straight, forms the front edge of this part of the paddle; it is smooth, transversely rounded, and non-articular. At its distal end a very short convex articular surface is intercalated between it and the long directly distal surface. The following are its dimensions in inches : — Preaxial border 3.7 ; proximal border 4.8 ; longer distal border 3.1 (its articular surface is concave from its dorsal to its ventral margins) ; shortest border, between the last and the preaxial one (having a smooth convex surface), 1.5. From the preaxial position of this bone, it is manifestly the tibia.

The first postaxial bone (g) is also a pentahedron ; its long transverse diameter is 4.6 inches, and its short or axial diameter 3 inches. Proximally it joins the first postaxial division of the distal surface of the femur. Its distal border is formed by two articular surfaces (concave in both diameters), which meet, a little behind the short axis of the bone, in a salient angle. The line of union of the mesial border of this bone with the tibia nearly cuts the distal angle of the femur.

To the postaxial border of this bone the second postaxial bone (h) (the third and hindmost one in the row) articulates. Its proximal border articulates throughout its entire length with the femur*. Its postaxial border is convex and non-articular, forming here the posterior border of the paddle; and its short distal (tarsal) articular border makes with that of the middle bone a deep reentering angle. The transverse diameter of this bone is 5.7, and its axial diameter 3.4 inches.

The characters of the early cervical vertebrae and the long tapering neck prove beyond doubt this spinal column to be that of a Plesiosaurus, and differentiate it from the subgenus Pliosaurus as hitherto defined. From the length of the column (in its present incompleteness 15 feet) Mr. Hansel's Plesiosaurus must have attained a size as great as, perhaps greater than, P. megadeirus ( Seeley), another Kimmeridge Plesiosaurus, represented by two series of associated bones from Haddenham and Ely, preserved in the Woodwardian Museum†. The absence of any published account of these fossils has prevented me from instituting so searching a comparison of them with Mr. Mansel's Plesiosaurus as I could have de-

border separates the proximal and posterior corner from the remainder of the bone. I am doubtful whether this is an accidental or a natural division ; if the latter, the piece so separated is a fourth enemial element.
 * A line running from near the outer end of this border to the posterior

† Catalogue of Ornithosauria, Aves, and Reptilia from the Secondary Strata, in the Woodwardian Museum, by H. G. Seeley, p. 97.