150 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



Order MARSUPIALIA. 



MARSUPIALS. 



Young at birth arc usually placed in an abdominal pouch formed 

 by a fold of skin about the milk glands of the mother, where they 

 remain for a considerable time. Reproductive organs of peculiar 

 structure in both sexe>, nearly all the parts being double in the 

 female. Brain small, the corpus callosum rudimentary. Heart 

 with two veiue. 



Suborder P0LYPR0T0D0NTIA. 



Incisors numerous, small, subequal. Canines larger than the incis- 

 ors. Molars with sharp cusps. {Flower mid Lydekker.) 



Family DIDELPHIID^B. 



OPOSSUMS. 



Incisors ^. Hind feet with the four outer toes subequal, distinct, 

 and a well-developed opposable hallux. 



Genus DIDELPHIS Linnseus (1758). 



Didelphis Li.w i:rs. Syst. Nat., 10th ed., I, 1758, i>. 54. 



Type. — Didelphis marsupialis Linnseus. 



Arboreal: feet not webbed. 



Dentition— 1.,^; C., j^; P., g^|; M., J } = :>o. 



KEY TO THE SPECIES OF DIDELPHIS FOUND ON THE BOUNDARY LINE." 



Tail black for basal third ; generally four-fifths the length of head and body or 

 more (tail ratio about 90-95) Didelphis mesamericana texensis (p. 150). 



Tail black only at extreme base; generally less than two-thirds the length of 

 head and body (tail ratio about To) Didelphis virginiana (p. 153). 



DIDELPHIS MESAMERICANA TEXENSIS (J. A. Allen). 

 TEXAS OPOSSUM. 



Didelphis mesamericana texensis J. A. Ai.i.kn. Bull. Amer. Mus. Nat. Hist.. 

 XIV, Art. XI. June 15, 1901, p. 172. 



Type-locality 9 . — Brownsville. Cameron County. Texas. 

 Type-specimen. Cat. No. U\U, U.S.N.M. 



Geographical distribution.- — The coast region of Texas, from Nue- 

 ces Bay southward, and the Lower Rio Grande Valley, as far up 



" See Preliminary Study of the Xorth American opossums of the Genus 

 Didelphis, by Dr. J. A. Allen. Lull. Am. Mus. Nat. Hist.. XIV. Art. XL pp. 140- 

 bss. June 15, 1901. 



