

372 Geological Society. 



PROCEEDINGS OF LEARNED SOCIETIES 



GEOLOGICAL SOCIETY. 



December 20, 1332.— J. W. Hulke, Esq., F.R.S., 



President, in the Chair. 



The following communication was read: 



"On Generic Characters in the Order Sauropterygia." By 

 Prof. Owen, C.B., F.R.S., F.G.S., &c. 



After referring to the subdivision of De la Beche's group of 

 Enaliosauria into the orders Ichthyopterygia and Sauropterygia, the 

 author indicated that the latter showed differences in the proportional 

 length of the neck and the number and form of its vertebrae bearing 

 relation to the size of the head, together with modifications of the 

 teeth, of the sterno-coraco-scapular frame and of the paddle-bones, 

 leading to the formation of two genera, namely Plesiosaurus and 

 Pliosaurm, the latter so called to indicate the nearer approach made 

 by it to a generalized Saurian type. In Crocodilia the crowns of 

 the teeth show a pair of strong enamel ridges, placed on opposite 

 sides of the teeth ; and these occur also in Pliosaurus, while in Plesio- 

 saurus they are not present. Pliosaurus further approaches the 

 fresh-water Saurians by the large size of the head and the shortness 

 of the neck. 



The author described the sterno-coraco-scapular frame in the 

 Sauropterygia generally as consisting chiefly of a pair of large 

 coracoid bones meeting in the middle in a straight suture, but separated 

 by a notch anteriorly and posteriorly ; in front of these is an 

 episternum, also notched in front ; and attached to this on each side is 

 a scapula, directed outward and backward, joined at its distal part 

 by suture to the antero-lateral margin of the coracoid, and forming 

 the outer border of the t; coraco-scapular vacuity/' a rounded aperture 

 which exists on each side in the fore part of the sterno-coraco- 

 scapular mass. The humeral articulation is formed by the outer 

 margin of the fore part of the coracoid and the extremity of the 

 scapula on each side. The chief distinctive character in Pliosaurus 

 consists in the retention of a typical character of the scapula which 

 is lost in the more specialized Plesiosaurian forms, namely the pro- 

 duction of part of the blade-bone laterad and dorsad, where it 

 terminates freely, this portion representing the main body of the 

 scapula in the higher vertebrates. In Pliosaurus this portion is 

 separated by a large notch from that which in both genera joins the 

 coracoid and assists to form the glenoid cavity. The latter portion 

 also extends further mesiad than in the Plesiosaurs, so that its 

 sutural border unites with the fore end of the coracoid, which is 

 much produced forward. The author finds the true homology of 

 the constituents of this sterno-coraco-scapular mass in the endo- 





