37 
Ichthyosauria. 
The humerus and femur are relatively short, bat the radius 
and tibia are still shorter, and may be reduced to oblong bones 
in which the breadth is greater than the length. The humerus 
has no foramen. Usually the anterior pair of (pectoral) paddles 
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. 
o oo 
Bio. 46. — (a) Dorsal aspect ol the left pectoral, and (b) ventral aspect of the right pelvic 
limb of Ichthyosaurus intermedins (Conybeare) ; Lower Lias, Lyme Regis, Dorsetshire. 
A. h, humerus; r, radius; u, ulna ; r 1, radiale ; i , intermedium; u I, ulnare; cl, 
c 2, eentralia; B. /, femur; .t, tibia; ./, flbula; 1 1, tibiale ; /l, flbulare; 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 in 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 Rdnetic to the Chalk inclusive ( see Table of Stratified 
Hocks, p. x.), but they occur in the greatest abundance, both as 
Wall-cases, 
No. 14. 
Table-case3, 
Nos. 13, 14. 
