A grammar of the English language :

p. 152

. > § 120. 1. Pure trochaic tetrameter consists of lines containing four trochees each, the trochee being sometimes replaced by a pyrrhic.

But the most common form of trochaic tetrameter

p. 153

The following is an example of trochaic tetra- meter catalectic, alternating with trochaic tetra- meter.

In lyric poetry we often find the trochaic tetra- meter catalectic without the alternating line of full tetrameter. .

—The combination of a line of trochaic tetrameter with one of trochaic tetrameter catalectic, forms a verse of seven trochaic feet with a catalectic syllable.