166 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



Superorder MONODELPHIA. 



Young not born until of considerable size and nearly perfect de- 

 velopment, deriving their nourishment before birth from the mother 

 through the intervention of a placenta; a well-developed corpus 

 callosum. {D. S. Jordan.) 



Order EDENTATA. 



The name assigned to this group by Cuvier is often objected to as 

 inappropriate— for although some of the members are edentulous, 

 others have very numerous teeth. If the teeth are not always absent, 

 they invariably exhibit certain imperfections, which are indeed 

 almost the only common characters binding together the various 

 extinct and existing members of the order. These are that they are 

 homodont and, with the remarkable exceptions of Tatusia and Oryo- 

 teropus, monophyodont ; they are never rooted, but have persistent 

 pulps; except in some fossil forms, they are always deficient in the 

 enamel. {Flower and Lydekker, abridged.) 



Family DASYPODIDtE. 



.ARKASIILOS. 



The greater part of the skin strongly ossified. Teeth numerous, 

 simple, of persistent growth, and usually monophyodont, but in one 

 genus {Tatusia\^ = Tatii^) a succession of teeth has been observed. 

 Zyogmatic arch of skull complete. Fore feet with strongly devel- 

 oped, curved claws, adapted for digging and scratching — three, four, 

 or five in number. Hind feet plantigrade, with five toes, all pro- 

 vided with nails. 



Subfamily TA.TTJII(rJE;. 



. This group contains but one genus (Tatu). Teeth f or ^, very 

 small, subcylindrical. The first and second subcompressed, the last 

 considerably smaller than the others. With the exception of the 

 last, all preceded by two-rooted milk teeth, which are not changed 

 until the animal has nearly attained its full size. Body generally 

 elongated and narrow. Head narrow, with a long, narrow, sub- 

 cylindrical, obliquely truncated snout. Ears rather large, ovate, and 

 erect, placed close together on the occiput. Carapace with seven to 

 nine distinct movable bands. Tail moderate or long, gradually 

 tapering; its dermal scutes forming very distinct rings for the 

 greater part of its length. Fore feet with four visible toes and a 

 concealed clawless rudiment of the fifth. Claws all long, slightly 

 curved and very slender, the third and fourth subequal and alike, 

 the first and fourth much shorter. Hind feet with five toes, all 



