StTBORDER B 



therium beds) occur 

 Orophodon Ameghino. 



XENARTHRA 



97 



the incompletely known genera Octodontherium and 



Tribe 2. HICANODONTA Ameghino. ^ 



In all members of this group the endoskeleton is modified for the support 

 of a highly complex exoskeleton in which striking characters of generic 

 importance are present. But the tail sheath, usually made the chief basis 

 of distinction, does not show characters of greater value in classification than 

 any other part of the skeleton. 



The tribe is separated at present into four families, the genera of which 

 share many characters in common, chiefly of the exoskeleton. Were the 

 endoskeleton as well known, less difficulty would be experienced in classi- 

 fication. Without doubt the Glyptodontidae and Sclerocalyptidae include genera 

 that pertain to other families, but they cannot at present be separated. 



Family 1. Glyptodontidae. 



Glyptodon Owen (Figs. 120, 121). Head truncated, with nasals short and 

 small. Teeth trilobate throughout, with vaso-dentine markedly branched. 

 Humerus without entepicondylar foramen. Manus with four digits. 



Fig. 120. 



Glyptodon reticulatus Owen { = Schistopleurmn typus Nodot). Pampas formation of Eio Saladb, Argentina. 

 Restored skeleton with shell in the Museum at Paris. 1/25. (After Gaudry.) 



Pes with five digits. Pubis comparatively small with cross-bars united by 

 cartilage. Head shield plates separate. Carapace large, robust and nearly 

 hemispherical, without anterior lateral prolongation. Caudal sheath short 

 and conical, composed of nine to ten rings with distal plates of each ring 

 large and tuberculate. Pleistocene of Argentina, Bolivia and Brazil. 



Glyptotherium Osborn. Pubis greatly reduced, cross-bar vestigial or absent. 

 Carapace medium-sized and elongate, without anterior prolongation. Plates 



^ The descriptions of this group and the arrangement of genera under family divisions are 

 extracted from the most recent classificatory key that has been published on armoured loths, 

 namely that by Barnum Brown as an Appendix to his description of Brachyostracon., in Bull, 

 Amer. Mus. Nat._Hist., vol. xxxi., 1912, pp. 167-177. 



VOL. ITI H 



