1892.] NATURAL SCIENCES OF PHILADELPHIA. 439 



resents the deuterocone and the only difference, therefore, consists 

 in the fact that the anterior horn of the inner crest is not developed 

 from the deuterocone, as in P4, but from the front margin of the 

 protocone or from the cingulum. 



X. AMBLYPODA. 



The oldest representative of this group is the Puerco genus 

 Pantolambda, in which the premolars have already attained quite 

 an advanced stage of differentiation. Except in Pi^ the superior 

 premolars consist of a crescentic and acute protocone which pro- 

 jects strongly toward the inner side of the tooth, and a crescentic deu- 

 terocone. Seen from the outside, the last three inferior premolars 

 seem to be simple, compressed and trenchant cones with metaconids 

 which become better marked as we pass from p^ to p*. But in 

 reality p^ supports a complete anterior V and a broad transverse 

 talon ; the V is less developed on p^ and very obscurely indicated 

 on p-. The superior premolars of Coryphodon show no advance 

 upon those of Pantolambda. The low^r premolars are in gen- 

 eral like those of the Puerco genus, but the species vary in the 

 completeness with which the cusps are distinguished. In ButJnno- 

 don radians the protoconid is concave externally and shows a dis- 

 tinct cusp on its Older side. 



In the Dinocerata the homologies of the cusps in both the molar 

 and premolar series are exceedingly obscure, owing not only to their 

 own peculiarities, which are very marked, but also to the lack of 

 any intermediate links by which to connect them with more typical 

 forms of teeth. It will, therefore, suffice to say that in this group, 

 with the exception of Bathyopsis, the first premolar in both jaws 

 has disappeared and that the remaining teeth in this series have 

 assumed the molar pattern. The crown is traversed by two ridges 

 which meet internally and thus form a V which opens outwardly. 

 Strange to say, this arrangement obtains in both upper and lower 

 teeth, the usual reversal of pattern not being found. 



XI. PROBOSCIDEA. 



The phylogeny of the elephants is still an unsolved problem and 

 we therefore know little as to the homologies of their molar cusps. 

 From several facts, however, we may infer that their molar teeth were 

 derived from a quadritubercular form. This condition is retained 

 in the premolars of Mastodon, upper and lower alike. In Dinothe- 



