356 SYNorsis of the vektebkate fauna of the puerco series. 



ti-ochlea is not oblique to the axes of tlie bone. Tlie head presents convex faces an- 

 teriorly interiorly. The anterior face is convex in every direction, and is continued 

 to the external side. The internal face is not separated from the anterior along- the 

 superior border, but is separated below and distally by a strong notch. This interior 

 facet indicates a large tibiale oi- "internal navicular,'' a bone well known in Rodentia, 

 and in Bathmodon among the Coryphodontidw. This fiicet is larger than in Peripty- 

 chus, and in the latter genus it is not cut oft' by a groove as in Ectoconus. The cal- 

 caneum has a very long tuber. The astragaline facets are in a general horizontal 

 plane, the internal (sustentaculum) small and a little concave; the external large, 

 wide, and a little convex. No distinct fibular facet. The cuboid facet is large, and 

 nearly anterior in presentation. The cuboid has the usual tuberosity, and also a large" 

 distal facet. 



The foot was evidently entirely plantigrade and penladactyle in this genus. 



In its dentition Ectoconus presents the most complex known form of the tritu- 

 bercular type. 



EcTooONUs DiTRiGONus Copc ; Aiuer. Naturalist, 1884, p. 790, tig. 4. Periptyclms ditrujoims Cope ; Tertiary Verte- 

 lirata, p. 404, PI. XXIII g, fig. la. Conoryctes dUrifjouus Cope ; Tertiary Vertebrata, 1885, PI. XXIX d, explana- 

 tion, and figs. 2-G. 



Thirty-two individuals of this species have been sent me, all from the Lower 

 Puerco beds. The most important of these include the teeth and all the dentigerous 

 bones, excepting the premaxillaries, with fragments of humerus, scapula and tibia 

 with calcaneiim, astragalus and cuboid elements entire. Of another, the proximal 

 parts of the astragalus and calcaneum are preserved with the heads of the first, a 

 median, and the fifth metatarsals. 



The dentition has been described so far as the molars and superior incisors arc 

 concerned. The first and second true molars usually possess eight cusps, but occa- 

 sionally there are nine, that is two external cingular cusps. The heels of the first 

 and second inferior premolai's arc tubercular, and the external cingulum of the infe- 

 rior true molars is well marked. The enamel is nearly smooth. 



The external (fibula) side of the astragalus is a vertical facet. The internal face 

 is nearly vertical. Beyond it a large depressed tuberosity projects a short distance 

 inwards but not posteriorly. It bounds tlie sustentacnlar facet of the astragalus 

 behind. This postsustentacular tuberosity is truncated inwards and downwards {)os- 

 teriorly. The sustentacnlar pi'ocess of the calcaneum projects outwards and forwards 

 in a subcirciilar rim beyond the smaller subround facet. The external facet forms 

 about one-fifth of a circular band, the concavity being next the middle of the proxi- 



