OPTHALMOSAURUS PLEYDELLI. 9 



furnished with a groove to receive the anterior end of the coracoid, 

 which is more than usually expanded, and is united to its fellow by 

 a cartilage ; only the right one has the anterior notch, which is a 

 characteristic of the coracoid bones of the Ichthyosaurus. 



The scapula is curved throughout, the concave side being inward 

 so as to overlap the ribs. The limbs of the Order Ichthyopterygia 

 show, as might be expected, a remarkable deviation from the lacertine 

 type to adapt it for pelagic life, they are specially formed for 

 strength, combined with elasticity. The phalangeal bones, instead 

 of being elongated as with Pliosaurus and Plesiosaurus^Q polygonal 

 and arranged in more than five closely-packed longitudinal rows, 

 the whole covered with an integument forming a highly elastic 

 organ of locomotion. The anterior border of the integument was 

 furnished with a narrow band covered with minute horny scales, the 

 band of the posterior border was broader, containing apparently parallel 

 bands of muscles set obliquely to the axis of the paddle. In the Lati- 

 pinnate group, which ranges from the lias to the chalk, these integu- 

 mental borders only reached a short distance below the terminal 

 digits; whereas in the Longipinnate group, which is not found above 

 the lias, the borders were produced to a point a long distance below. 



The humerus of the Order is a short massive bone, and usually 

 larger than the femur ; the distal ends of both are much broader 

 than the proximal, which is twisted forward through an angle of 

 40. The humerus and femur of Ichthyosaurus are furnished 

 with two facets to receive the ulna and radius, which are close 

 to each other; to these are articulated inferiorly three bones 

 the ulnare, intermedium, and radiate ; the intermedium being the 

 middle bone, and articulates with the radius and ulna at its 

 junction. Below the intermedium is the centrale, and below again 

 the remaining metacarpals and phalangeals. The humerus of 

 OpJithalmosaurus was furnished with three facets, to which three 

 bones of the forearm were severally attached. The homology of 

 this third bone in the paddle of Oplitlialmosaurus becomes a very 

 interesting question. The peculiarity of three facets to the 

 propodial bones (humerus and femur) occurs in the Kimmer- 



