486 Professor H. G. Seeky — Dentition oj Cynognathns. 



The question naturally arises witli regard to the above table, which 

 of the above characteristics shall be taken as determinative in drawing 

 the lines ? The writer may be prejudiced by his studies of connate 

 waters, but he feels very strongly that a marked point in the chemical 

 evolution of the ocean, which must be practically nearly universal 

 and coeval, makes the best of dividing lines. So he would put the 

 beginning of the Cambrian at the time the concentration of the ocean 

 passed the physiological optimum (somewhere between six and eight 

 parts per thousand), and the secretion of hard parts by living 

 organisms began, and he would put the beginning of the age previous 

 when the water supplied to the ocean became alkaline, and hence the 

 accumulation of chlorides of lime, magnesia, and iron was checked, 

 and he believes that was due to the first great extension of living 

 vegetation over the surface of the land. He does not believe it 

 purely accidental that massive beds of dolomite, of chert and iron, 

 i.e. jaspilite, and of black slate appear in about the same series. 



II. — On the Dentition of the Palate in the South Afeican 

 Fossil Reptile Genus Ctxogxathvs. 



By Prof. H. G. Seeley, F.R.S., F.G.S., King's College, London. 



(PLATE XXIV.) 



rPHE Cynodont reptilia from the Lower Karroo rocks of South 

 J. Africa, characterized by relatively large incisors and relatively 

 small, sharp-pointed, molar teeth, were grouped under the type genus 

 Lycosaurus as Lycosauria. The removal of matrix from the palate of 

 ^lurosattrus showed that in one member of the group at least the 

 palate carries patches of teeth, each of which has the form of a small 

 blunt flattened cone. From the fact that no Cynodont skull is 

 available in which the mandible is free from the head, the nature of 

 the palatal dentition is imperfectly known. 



Of the new Cynodont reptilia obtained by myself from the Upper 

 Karroo rocks in 1889, the most complete were species of Cynognathns 

 (Phil. Trans. Royal Soc, B, 1895, p, 59). But these specimens, with 

 relatively large denticulated molar teeth, all have the mandible closed 

 upon the skull, so that the anterior part of the palate is not displayed. 



In Cynoynathis crateronotus (op. cit., fig. 9, p. 83) the palatine bones 

 arch over the palato-nares, but as they extend backward laterally 

 each appears to be twisted over, with a lateral bulge, to make the 

 walls of the palato-nares behind the hard palate. The mandibular 

 symphysis obscures the front of the palate, but it only extends 

 posteriorly as far as the maxillary canines. No teeth were exposed 

 upon the maxillary plates of the palate. The matrix is so intractable 

 and the bones so friable in the figured species C. Berryi that no 

 attempt can be made to expose the palate with the chisel. In this 

 species the extremity of the snout is lost. But the weathered nasal 

 chamber shows a vertical median plate of bone (op. cit., fig. 24, p. 124) 

 which appears to enter into the palate, rising for some distance into 

 the nasal chamber, where it is flanked by thin, curved plates which 

 may represent turbinal bones. It is less than VV inch wide, separated 



