OP ENDOTHIODON BATHYSTOMA. 



479 



crowns was not shown. From the forms of their bases it seemed 

 not improbable that they might resemble the teeth of Placodus. 

 The present specimen has the crowns perfectly preserved. The 

 longest are more than 2'b centim. high. They are compressed from 

 side to side, of a long lanceolate form, with strong transverse 

 serrations on the anterior and posterior margins. 



The dentigerous area is obliquely inclined on the Lacertilian plan, 

 and the different groups of teeth, instead of being arranged from the 

 front backward, as in Theriodonts, succeed each other in the opposite 

 or transverse direction. In front and external to the teeth is a con- 

 cave area 2*25 centim. wide anteriorly, limited by the buccal margin 

 of the bone externally, and bordered internally by a short sharp 

 longitudinal ridge, which prolongs the line of the dentigerous area 

 forward. The concave space between these ridges is prolonged 

 backward external to the teeth, becoming narrower. The first or 

 external row of teeth, which may be incisors, are apparently six in 

 number ; the crowns are compressed from side to side, rather wider 

 and shorter than in the other parts of the series. The second or 

 premolar series is counted with difficulty, but appears to number 

 10 teeth. In no case is the summit of the crown preserved, but 

 the anterior teeth have been worn obliquely on the external side by, 

 the teeth in the upper jaw. This condition is well shown in three 

 anterior crowns. The third or molar 

 row apparently includes 15 teeth. In 

 this series the serration of the crown 

 is seen. It has been observed in nearly 

 all the crowns, but from the nature of 

 the matrix it becomes removed in 

 process of development. There is no 

 evidence that it extended below the 

 upper half of the crown. 



There is a fourth row of six teeth 

 developed on the inner anterior border. 

 These teeth descend in position, as do 

 the hinder molars, as they extend back- 

 ward. , The two middle series are 

 between and behind the short internal 

 and external series, which converge 

 forward ; it is possible that this anterior 

 inner group may represent a series 

 of canines, more perfectly developed 

 than among lizards. There is remark- 

 ably little variation in the forms and 

 characters of the teeth in the several 

 rows ; so that if the tooth-rows bear the interpretation suggested for 

 tbem, it must rest upon their grouping, and not upon differentiation. 

 The roots of the teeth are in sockets, embedded deep in the jaw. 



In no Anomodont or other reptile has a jaw been described which 

 in any way resembles this in form, muscular attachment, position 

 of the articulation, and form and arrangement of the teeth. 



2J.2 



Fig. 3. — Teeth {enlarged) 

 showing serfxitwns. 



WS^ 



■^y 





nat. size. 



