Section I. MONOCYRTIDA, Haeckel, 1862, Monogr. d. Radiol., pp. 280, 281.
Definition.—Cyrtoidea monothalamia, with simple, not jointed shell (or cephalis), without transverse constrictions.
Synopsis of the three Families and six Subfamilies of Monocyrtida.
Family LIX. Tripocalpida. Three radial apophyses. |  | Mouth open, | 1. Archipilida. |
| Mouth closed, | 2. Archiperida. | ||
Family LX. Phænocalpida. Numerous radial apophyses. | | Mouth open, | 3. Archiphormida. |
| Mouth closed, | 4. Archiphænida. | ||
Family LXI. Cyrtocalpida. No radial apophyses. | | Mouth open, | 5. Archicorida. |
| Mouth closed, | 6. Archicapsida. |
Family LIX. Tripocalpida. Three radial apophyses. | ||||
| Mouth open, | ||||
| 1. Archipilida. | ||||
| Mouth closed, | ||||
| 2. Archiperida. | ||||
Family LX. Phænocalpida. Numerous radial apophyses. | ||||
| Mouth open, | ||||
| 3. Archiphormida. | ||||
| Mouth closed, | ||||
| 4. Archiphænida. | ||||
Family LXI. Cyrtocalpida. No radial apophyses. | ||||
| Mouth open, | ||||
| 5. Archicorida. | ||||
| Mouth closed, | ||||
| 6. Archicapsida. | ||||
Family LIX. Tripocalpida, n. fam.
Archipilida et Archiperida, Haeckel, 1881, Prodromus, pp. 427, 429.
Definition.—Monocyrtida triradiata. (Cyrtoidea with a simple, not jointed shell, representing a simple cephalis, with three radial apophyses.)
The family Tripocalpida, composed of the Archipilida and Archiperida of my Prodromus, comprises those Cyrtoidea in which the lattice-shell is quite simple, without transverse constriction, and bears three radial apophyses. The two subfamilies differ in the shape of the basal mouth, which in the Archipilida is a simple wide opening, in the Archiperida closed by a lattice-plate; the former are here divided into eight, the latter into seven different genera.