52 Geological Society. 



of Scandinavia, which some Continental geologists correlate with 

 the Riss Stage of the Alps. 



In that case, the main local drift of the north-eastern coast falls 

 into the third and last Glacial Period of Northern Europe. The 

 evidence for Interglacial lapses in the local drifts is very in- 

 conclusive. 



All the observed features seem to point to the fact that the 

 Scandinavian ice-sheet advanced on the east coast of England in 

 the same way as it invaded Northern Europe round the southern 

 shores of the Baltic, and gave rise to analogous climatic conditions 

 leading to the formation of loess, a fragment of which is found 

 protected from the erosive action of the later local glaciation in a 

 small hollow on the Durham coast. 



June 4th, 1919.— Mr. G. W. Lamplugh, F.R S., 

 President, in the Chair. 



The following communication was read: — 



' On the Dentition of the Petalodont Shark, Climaxodux.' 

 By Arthur Smith Woodward, LL.D., F.R.S., P.L.S., F.G.S. 



The author describes the nearly complete dentition of a new 

 species of Climaxodus from the Calciferous Sandstone of Calder- 

 side, near East Kilbride (Lanarkshire), now in the Roj'al Scottish 

 Museum, Edinburgh. Nearly all the teeth are borne on the 

 symphysis of the jaw, only the outer paired longitudinal series 

 extending a little farther back over the rami. There are from 

 three to five longitudinal series, each of five or six teeth of the 

 ordinary Climaxod as-type, covering the greater part of the sym- 

 physis ; and the Hanking paired series, which extends farther 

 back, comprises more depressed teeth, in which the cutting-edge 

 forms a low blunt ridge. The two jaws are nearly similar ; but, as 

 in Janassa, the upper seems to have been slightly wider than the 

 lower jaw. The teeth rapidly increase in size backwards, also as 

 in Janassa, but they must have been all retained in the mouth 

 throughout life ; while in Janassa only a single transverse row 

 would be in function at one time, the .older teeth being thrust 

 beneath to form a supporting base. Climaxodus and Janassa 

 are thus two distinct genera. These Petalodonts are especially 

 noteworthy among the Elasmobranchii, because during the greater 

 part of the life of each individual there cannot have been more 

 than six or eight teeth in succession, a condition remarkably 

 different from that in all ordinary sharks and skates in which 

 the successional teeth are always very numerous and rapidly 

 replaced. The same limited tooth-succession is to be observed 

 in the Carboniferous Cochliodontida?, and perhaps also in the 

 contemporaneous Psammodontida?. Most of the teeth of Cli- 

 maxodus are also interesting as showing a restricted area of 

 highly vascular dentine much resembling a tritor in the dental 

 plate of an ordinary Chimajroid. This character in Elasmobranch 

 teeth which are peculiar for their slow and scanty succession, may 

 have some special significance in connexion with the origin of the 

 Chimseroids. 



