HEPTODON. 655 



This specimen demonstrates three prominent characters of the species: 

 (1) There is no rib of the external wall of the superior molars dividing the 

 areas that belong to the crescents respectively; (2) the transverse crests of 

 the true molars are perfectlj^ continuous; (3) the first premolar is two-rooted 

 (it is represented as two-rooted, by Pict^t, in the Pacliy)wIo2)hus duvali). 

 The middle angle or summit of the anterior external crescent of the molars 

 is a trihedral cusp, and it is well separated from the anterior cingular cusp. 

 The transverse crests are curved obliquely backwards. On the premolars 

 it is the posterior transverse crest that is wanting, and the width of the 

 crown is maintained by a posterior basal cingulum not distinct in the true 

 molars The premolars have less anteroposterior extent than the true 

 molars, and they diminish in transverse extent anteriorly, so that the base 

 of the crown of the first is anteroposteriorly wedge-shaped. The last three 

 premolars have two external cusps joined together at the base, the posterior 

 being rudimental on the second premolar. There is a considerable diastema 

 between the canine alveolus and the first premolar. 



The transverse crests of the third inferior true molar are without inter- 

 ruption, and the second sends a descending ridge forwards from each end. 

 The heel is small, supporting a single cusp which rises from its posterior 

 margin. It is larger than in the P. calciculus. 



Measurements. 



M. 



Length of maxillary bone from canine 074 



Length of diastema OtC 



Length of four premolars on bases 027 



Length of bases of three true molars 0320 



Length of bases of first premolar 0076 



_. ^ „ , , < transverse 0070 



Diameters of second premolar { ,^„.,^ 



( anteroposterior 00/0 



_. , I. !• .-. 1 < transverse 0100 



Diameters of fourth premolar i 



( anteroposterior 0080 



Diameters of second true molar J ■ ' 



( transverse 0125 



.^. , n ^, ■ , . , (anteroposterior 0114 



Diameters of thud tnie molar.; '^ „,„^ 



( transverse 0130 



Length of heel of third inferior true molar 0032 



Width of second crest of third inferior true molar 0074 



Part of the left mandibular ramus, supporting five molar teeth, served 

 as the first indication of this species. The last true molar is wanting. The 

 second premolar has a short heel with a median cusp rising from its poste- 



