Naturgeschichte der Säagethiere während des Jahres 1884. 131 

 Die Periptychidae umfassen 7 Gattungen: 



1. Three premolars. 



a. Fourth superior premolar like molars; inferior premolars without 

 internal ledge: Hexodon. 



2. Superior molars with intermediate tubercles, and tubercles anterior 

 and posterior to the internal cusp; four premolars. 



a. Superior molars with an external cingular cusp; inferior premolars 

 without internal ledge: Ecloconns. 



b. No supplementär}- external cusps , inferior premolars with internal 

 ledges : Periptychus. 



3. Intermediate tubercles wanting; four inferior premolars, without 

 internal lobes. 



a. Superior molars with posterior internal cusp only, besides internal 

 V; last two superior premolars with internal lobes: Anisonchus. 



b. Superior molars with internal V only, no other internal lobes; last 

 two superior premolars with internal cusps: Hemithlaetis. 



c. Superior molars with posterior internal cusps only, besides apex 

 of V ; fourth superior premolar only with internal lobe : Haploconus. 



4. Superior molars unknown; inferior premolar No IV? with two opposed 

 crescents and a heel. 



Inferior molars with one or two pairs of opposed crescents: Zetodun. 



Alle bekannten Arten der Periptychidae stammen aus dem 

 Puerco-Eocän. — Die Phenacodontidae, welche theils der Puerco-, 

 in grösserer Zahl aber der Wasatch-Epoche angehören, zerlegt 

 Verf. in 4 Gattungen: 



Last superior premolars with but one external cusp; in- 

 ferior molars with Vs: Protogonia. 



Last superior premolars with two external cusps; inferior 

 molars with well-developed cusps: Phenacodus, 



Inferior molars with flat grinding faces; no cusps: A7iacodon, 



Second, third and fourth superior premolars with two ex- 

 ternal cusps; those of inferior molars well developed: Diacodexis, 



Die Meni<icotheriidae basiren auf dem einzigen genus Mejü- 

 scotJierium, dessen drei Arten der Wasatch-Epoche angehören. 

 Zahlreiche Holzschnitte erläutern die Charactere der einzelnen 

 Gattungen und Arten; darunter sind Abbildungen vollständiger 

 Skelette von Phmacodus primaevus und Vortmanni; Amer. Natural. 

 Bd. 18 p. 790-805 und p. 892-906 T. 28—30. 



Derselbe beschreibt Anisonchus agapetülns und cophater n. 

 foss. Arten aus der Puerco -Epoche; Proc. Amer. Phil. Soc. 

 Philad. Bd. 21 p. 320—321. 



