242 .Prof. II. G. Seelcij — LahijrintJtodontfrom S. Africa. 



the lower part of the crown, where the number of ribs is greater. 

 They do not often show dichotomous division ; but the ribs which 

 rise from the base irregularly die away in the grooves. They have 

 an appearance of being finer and more numerous in the lower 

 part of the crown than at the transverse fracture, where thej- 

 number about eight3^ There is practically no enamel on the crown, 

 which shows only a faint surface gloss. On receiving the tooth 

 I had a cast made, and a transverse section was prepared so as to 

 show the labyrinthic structure of the crown. The cut surface 

 now has the appearance of being bordered at the circumference 

 by close-set tubes which correspond to the external vertical ribs. 

 Under the microscope these sections of the reed-like sheath of the tooth 

 are mostly sub-quadrate, and hollow ; separated from each other by 

 a narrow band which passes inward and folds into the labyrinthic 

 substance of the tooth. The centre of the crown of the tooth is 

 occupied by the pulp cavity, nearly circular, slightly longer than 

 wide ; with a number of fine films at irregular intervals, radiating 

 outward from it as vertical plates dividing the folded tooth substance. 



The folding of the dentine is more complicated than in any genus 

 yet examined. Counting from the inner border there are about 

 twenty-five folded labyrinthic plates of dentine, which radiate to the 

 circumference, without greatly varying in width. Each of these 

 plates is made up of twelve or more alternate folds to right and left of 

 the tooth substance, with each fold often plicated, and including 

 spaces more or less small, frequently ovate, sometimes more elongated. 

 The dentine is composed of tubes which show a radiating arrangement 

 in harmony with the curvature of the folds. Each layer bears a thin 

 film upon its external infolded surface which appears to correspond in 

 position to enamel. This layer passes outward between the folds of 

 dentine, and appears to extend over the external surface of the tooth, 

 though most of the enamel is manifestly lost. Between the folded 

 plates are a series of supplementary wedge-shaped folds, about half 

 as numerous, which are continuous with the dentine of the plates on 

 each side, sometimes by its being folded over on the one side, and 

 connected hj anastomosis on the other side. 



The most distinctive features of the tooth are : ( 1 ) the external 

 layer of vertical tubes of dentine ; (2) the denseness of the folding of. 

 the dentine ; (3) the connection of the folds with each other in ways 

 different to those known in Mastodonsaurics ; and (4) the number of 

 small vacuities included in the folds of the dentine. 



The only clue to the form of the skull is given by the small palatal 

 vacuity, presumably palato-nasal, which descends upon the base of 

 the tooth, and may be evidence that the skull was broad, depressed 

 convex in front, with the nares in a forward position. The only genus 

 with the skull of this type hitherto indicated is the imperfectly known 

 Batrachio&uchus of Dr. R. Broom ; but that tj'pe is far too small to 

 have carried teeth of this size, which may indicate a skull twice as 

 large, or about 18 inches long. The teeth in JBatrachiosiichus are 

 undescribed. I do not anticipate that it will prove referable to 

 Ptychosphenodon (Geol. Mag., 1907, Dec. ^\ Yol. IV, p. 433), but it 

 is from an animal equally large. 



