There are three major groups of mammals, categorized on the basis of their see concept 34.6 ( page 739)

There are three major groups of mammals, categorized on the basis of their method of reproduction. Monotremes lay eggs to have children instead of having the mother bear them. The second type of mammal is the marsupial, which are non-placental animals who carry their young in their pouches. Eutherians are the third group who are placental mammals.

The title of Roderick's macabre song is "The Haunted Palace."  The words reflect the brother and sister's existence in the House of Usher.

Explanation:

In Stanza 1, Roderick croons about the keepers of the palace, which "good angels tenated," a reference to himself and Madeline.

Stanza 2 recalls their life in the "glory days" in the stately home: " Banners yellow, glorious, golden/ on its roof did float and flow."

The next stanza finds Roderick reminiscing about how everyone who happened to see him and his sister could not fail to recognize their bliss.  They were "(s)pirits moving musically."  

By Stanza 5, the evil has started to seep into the happy home: "Evil things, in robes of sorrow, /Assailed the monarch's high estate."

The concluding stanza speaks of the isolation, physically, emotionally, and spiritually of Roderick and Madeline Usher:

And travellers now within that valley,

Through the red-litten windows, see

To a discordant melody;

Through the pale door,

And laugh—but smile no more.