Ichthyosauria. 



37 



The humerus and femur are relatively short, but the radius Wall-cases, 

 and tibia are still shorter, and may be reduced to oblong bones No - 14 =- 

 in which the breadth is greater than the length. The humerus Table-cases, 

 has no foramen. Usually the anterior pair of (pectoral) paddles Nos * ' * 

 is the larger (see Figs. 45 A, B; and 46 A, B). The humerus 

 and femur in this order are unique in that, instead of having 

 convex condyles for the articulation of the fore-arm (radius and 

 ulna) they present distinct concavities for their reception. 



*"IG. 46. (A) Dorsal aspect ot the left pectoral, and (B) ventral aspect of the right pelvic 

 limb of Ichthyosaurus intermedius (Conyheare) ; Lower Lias, Lyme Regis, Dorsetshire. 

 A. /t, humerus; r, radius; u, ulna ; r 1, radiale ; i, intermedium; ul, ulnare; c 1, 

 c2, oentralia; B. /, femur; .(, tibia; ./, fibula; tl, tibiale; /I, fibulare; i, inter- 

 medium. 



These old marine lizards must have exercised the same 

 repressive action over the teeming animal population of the old 

 Liassic seas that the sharks do iu our seas at the present day. 

 They existed during the long period of geological time repre- 

 sented by the several formations extending from the Upper 

 Trias and Bhaetic to the Chalk inclusive (see Table of Stratified 

 Bocks, p. x.), but they occur in the greatest abundance, both as 



