Under the general head of cirrus we have found nine distinct forms—
1. Cirro-nebula (Ley) (Plates [2] and [3]). Cirrus veil.
Characterized by comparative absence of structure and by the formation of halo. Ci. Na.
2. Cirro-filum (Ley) (Plate [7]). Thread cirrus.
Built up of fine long threads, straight, curved, or crossing, but free from hazy curling or flocculent structures. Ci. F.
3. Cirrus excelsus (Plate [5]). High cirrus.
Characterized by great altitude, thinness, irregular branching structure. Ci. Ex.
4. Cirrus ventosus (Plate [6]). Windy cirrus.
Characterized by curving branches leaning forward in the direction of movement, and other long curving streamers lagging behind and below. Fluffy parts are usually present, and mark the origins of the long curling fibres. Ci. V.