Geological Society of London. 91 
some writers to glaciers, and that it is doubtful if the work of actual 
excavation has been accomplished by them at all. The differential 
movement of glaciers he attributed to three causes: (1) cracking and 
regelation (Tyndall and Helmholtz); (2) generation of heat by friction 
within the glacier (Helmholtz); (3) the penetration of the glacier by 
luminous solar energy, the absorption of this by opaque bodies con- 
tained in the ice (stones, earth, organic germs, etc.), and the trans- 
formation of it in this way into heat. To this last he attributed the 
greater differential movement of the glacier (a) by day than by night, 
(b) in summer than in winter. 
II.—December 20, 1882.—1. ‘‘On Generic Characters in the Order 
Sauropterygia.”” By Prof. Owen, C.B., F.R.S., F.G.S., ete. 
After referring to the subdivision of De la Beche’s group of Enalio- 
sauria 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 vertebree bearing relation 
to the size of the head, together with modifications of the teeth, to the 
sterno-coraco-scapular frame and of the paddle-bones, leading to the 
formation of two genera, namely, Plestosaurus and Pliosaurus, 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 Plesvosaurus 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 Sauro- 
pterygia generally as consisting chiefly of a pair of large caracoid 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 caracoid, and forming the outer border 
of the “‘caraco-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 caracoid and the extremity of the scapula on each side. ‘he chief 
distinctive character in Pliosawrus, consists in the retention of a typical 
character of the scapula which is lost in the more specialized Pleiso- 
saurian forms, namely, the production 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 Pliosawrus this 
portion is separated by a large notch from that which in both genera 
joins the caracoid 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 caracoid, which is much 
produced forward. The author finds the true homology of the con- 
stituents of this sterno-coraco-scapular mass in the endo-skeleton of the 
Chelonia; Piiosaurus shows characters resembling those of contem- 
porary Crocodilia. A third modification of the Sauropterygian type is 
indicated by teeth and a portion of the skull upon which the genus 
Polyptychodon has been founded. 
