338 E. L. Troxell — American Bothriodonts. 



This cingulum is broken on the inner surface. P^ is very 

 rugose, with a strong external cingulum leading to the 

 well marked tritocone and forming a double ridge 

 anteriorly on the protocone. 



A. deflectus can be further characterized, in general, by 

 the form of P^ with its external cingulum, small cuspid 

 dueterocone, and its rounded anterior and pointed pos- 

 terior ends ; by the boldness of the teeth in the manner 

 in which the cusps and cingular ridges stand out ; by the 

 position of the posterior nares situated just back of the 

 molars; by the long diastema in front of P^ and the 

 probable absence of P^. 



Very extensive lateral crushing has taken place in this 

 type specimen but it is evident that the skull was very nar- 

 row originally ; across between the orbits the distance is 

 scarcely more than 70 mm. The otic bullae are elongated 

 antero-posteriorly ; the occipital condyles are light, and 

 the supra-occipital is narrow (22 mm.). The face is bent 

 down strongly on the basicranial axis. The paroccipitals 

 form peculiar, strong ridges outside the paramastoid 

 processes ; the slender processes are near the condyles 

 and join the bullae at their bases. The sutures between 

 the frontals and parietals are not marked by ridges. 

 Marsh has pointed out that the postorbital processes are 

 long and more nearly close the orbit behind than is usual. 



The lower jaws of A. deflectus (fig. 7) are most inter- 

 esting in the number of small tubercles and interrupted 

 cingula around and between the lobes of the teeth. The 

 purpose of these seems to be to retard the movement of 

 food when the long points of the superior molars press 

 down between the lobes. 



On the inner side of the talonid of M3 is a cingulum 

 made up of a series of cusps ; the talonid itself is a single 

 isolated pointed cone. Two exterior basal tubercles lie 

 between the talonid and hypoconid; they appear less 

 conspicuously between the protoconid and hypoconid. 

 Small roughened areas break the transverse valleys and 

 unite adjacent lobes in each case, while a strong cingulum 

 lies anteriorly on the tooth. 



P4 likewise has an irregular lot of tubercles forming 

 the heel and has sharp ridges running to the point of the 

 protoconid ; ' only the outer side of this cone is smooth. 

 The paraconid marks the beginning of the sharp ridge to 

 the central cone. The tooth measures 21.3 X 13.7 mm. 



P3 is narrow with two straight ridges running to the 



