518 Prof. H. G. Seeley. On the Strw [May 14, 



It would thus appear that by studying the extinction curves it may 

 be possible to approximate to the three positions in the spectrum 

 which the colours giving the nearest approach to the three fuuda- 

 mental sensations on the Young-Hetmholtz theory occupy. 



III. " Researches on the Structure, Organisation, and Classifica- 

 tion of the Fossil Reptilia. VII. Further Observations on 

 Pareiasaurus" By H. G. SEELEY, F.R.S., Professor of 

 Geography in King's College, London. Received May 5, 

 1891. 



(Abstract.) 



The author distinguishes five zones of life in the Karoo rocks, 

 which are termed, counting from the bottom, Mesosaurian, Pareia- 

 saurian, Dicynodont, Theriodont, and Zanclodont. The Pareia- 

 saurian zone extends between the Prince Albert Road station and the 

 Nieuwveldt range of mountains. He obtained a nearly complete 

 skeleton from Bad, east of Tamboer, a less complete skeleton from 

 Tamboer Fontein, and a portion of jaw from near Klipfontein, on 

 the summit of the Nienwveldt range. These materials show almost 

 every part of the skeleton except some details of the carpus and 

 tarsus, and the number of digits. 



The skull shows in both specimens the structure of the palate, 

 which was closed in the median line, and almost covered with teeth, 

 which extend in four principal longitudinal rows on the vomera and 

 pterygoids. The teeth are slender, cylindrical, and recurved. There 

 are two oblique rows, half as long as the others, on the palatines. 

 They converge backward. Other teeth occur in rows behind these, 

 and in front of them. The posterior nares open behind the pterygoids 

 on the basi-sphenoid. The pterygoid bones diverge backwards to 

 meet the quadrate bones, which are wedged in between them and the 

 bones of the cheek. On the outer border of the side of the quadrate 

 is a perforation like that figured ' Phil Trans.,' B, 1889, PI. 10, fig. 4, 

 only smaller. The brain case has the same sort of relation to the 

 roof bones of the skull, as in marine Chelonia. The brain case is 

 depressed behind. The occipital condyle appeal's to be formed by 

 the basi-occipital in its lower half, and by the ex-occipitals in its 

 upper half. It is concave, and was margined below by a semi- 

 circular intercentral bone. A similar intercentral ossification occurs 

 behind it, below the atlas. The surface of the skull has no opening 

 except the nares, orbits, and the large parietal foramen. Its posterior 

 border is concavely notched. The surface shows the same pitted 

 and channeled ornament as in the specimen already described. 



The vertebral column is complete with the exception of a few small 

 terminal vertebrae of the tail. No neural arch has been found to the 



