II. Subfamily Diporaspida. Each radial spine with two opposite primary apophyses; therefore the whole shell with forty primary apophyses. |  | I. Tribe Phractaspida. Twenty radial spines without lattice-plates; no normal pores. |  | No by-spines, | 349. Phractaspis. | ||||
| With by-spines, | 350. Pleuraspis. | ||||||||
| II. Tribe Ceriaspida. Twenty radial spines all with lattice-plates produced by union of the branched apophyses of each plate. |  | Forty parmal pores (two in each plate)—no coronal pores in the plates. |  | Plates not dimpled, without network of crests. |  | No by-spines, | 351. Dorataspis. | ||
| With by-spines, | 352. Diporaspis. | ||||||||
| No by-spines, but free apophyses, | 353. Orophaspis. | ||||||||
| Plates dimpled, with a network of crests. |  | No by-spines, | 354. Ceriaspis. | ||||||
| With by-spines, | 355. Hystrichaspis. | ||||||||
| Eighty to two hundred or more parmal pores (in each plate two aspinal and two to ten or more coronal pores). | | No by-spines, | 356. Coscinaspis. | ||||||
| With by-spines, | 357. Acontaspis. | ||||||||
II. Subfamily Tessaraspida. Each radial spine with four crossed primary apophyses; therefore the whole shell with eighty primary apophyses. |  | III. Tribe Stauraspida. Twenty radial spines all or partly without lattice-plates. |  | All twenty spines without lattice-plates. | | No by-spines, | 358. Stauraspis. | ||
| With by-spines, | 359. Echinaspis. | ||||||||
| Four plates with, sixteen without, lattice-plates. |  | With by-spines, | 360. Zonaspis. | ||||||
| Twelve plates with, eight without, lattice-plates. | | With by-spines, | 361. Dodecaspis. | ||||||
| IV. Tribe Lychnaspida. Twenty radial spines all with lattice-plates (produced by union of the branched apophyses of each plate). | | Eighty parmal pores (four on each plate)—no coronal pores in the plates. |  | No by-spines, | 362. Tessaraspis. | ||||
| With by-spines, | 363. Lychnaspis. | ||||||||
| One hundred and sixty to three hundred or more parmal pores (in each plate four aspinal and four to twelve or more coronal pores). | | No by-spines, | 364. Icosaspis. | ||||||
| With by-spines, | 365. Hylaspis. | ||||||||
| I. Subfamily Diporaspida. Each radial spine with two opposite primary apophyses; therefore the whole shell with forty primary apophyses. | ||||||||||
| I. Tribe Phractaspida. Twenty radial spines without lattice-plates; no normal pores. | ||||||||||
| No by-spines, | ||||||||||
| 349. Phractaspis. | ||||||||||
| With by-spines, | ||||||||||
| 350. Pleuraspis. | ||||||||||
| II. Tribe Ceriaspida. Twenty radial spines all with lattice-plates produced by union of the branched apophyses of each plate. | ||||||||||
| Forty parmal pores (two in each plate)—no coronal pores in the plates. | ||||||||||
| Plates not dimpled, without network of crests. | ||||||||||
| No by-spines, | ||||||||||
| 351. Dorataspis. | ||||||||||
| With by-spines, | ||||||||||
| 352. Diporaspis. | ||||||||||
| No by-spines, but free apophyses, | ||||||||||
| 353. Orophaspis. | ||||||||||
| Plates dimpled, with a network of crests. | ||||||||||
| No by-spines, | ||||||||||
| 354. Ceriaspis. | ||||||||||
| With by-spines, | ||||||||||
| 355. Hystrichaspis. | ||||||||||
| Eighty to two hundred or more parmal pores (in each plate two aspinal and two to ten or more coronal pores). | ||||||||||
| No by-spines, | ||||||||||
| 356. Coscinaspis. | ||||||||||
| With by-spines, | ||||||||||
| 357. Acontaspis. | ||||||||||
| II. Subfamily Tessaraspida. Each radial spine with four crossed primary apophyses; therefore the whole shell with eighty primary apophyses. | ||||||||||
| III. Tribe Stauraspida. Twenty radial spines all or partly without lattice-plates. | ||||||||||
| All twenty spines without lattice-plates. | ||||||||||
| No by-spines, | ||||||||||
| 358. Stauraspis. | ||||||||||
| With by-spines, | ||||||||||
| 359. Echinaspis. | ||||||||||
| Four plates with, sixteen without, lattice-plates. | ||||||||||
| With by-spines, | ||||||||||
| 360. Zonaspis. | ||||||||||
| Twelve plates with, eight without, lattice-plates. | ||||||||||
| With by-spines, | ||||||||||
| 361. Dodecaspis. | ||||||||||
| IV. Tribe Lychnaspida Twenty radial spines all with lattice-plates (produced by union of the branched apophyses of each plate). | ||||||||||
| Eighty parmal pores (four on each plate)—no coronal pores in the plates. | ||||||||||
| No by-spines, | ||||||||||
| 362. Tessaraspis. | ||||||||||
| With by-spines, | ||||||||||
| 363. Lychnaspis. | ||||||||||
| One hundred and sixty to three hundred or more parmal pores (in each plate four aspinal and four to twelve or more coronal pores). | ||||||||||
| No by-spines, | ||||||||||
| 364. Icosaspis. | ||||||||||
| With by-spines, | ||||||||||
| 365. Hylaspis. | ||||||||||
Subfamily 1. Diporaspida, Haeckel.
Definition.—Dorataspida with twenty radial spines, each of which bears two opposite apophyses. The spherical shell is composed either of the meeting branches of these apophyses (Phractaspida), or of twenty perforated plates, produced by concrescence of their branches (Ceriaspida).
A. Tribe I. Phractaspida, Haeckel.
Definition.—Dorataspida without perforated plates; the spherical shell is composed only of the meeting branches of the two opposite apophyses, which arise from each radial spine. Therefore the meshes of the shell are all sutural.
Genus 349. Phractaspis,[[389]] Haeckel, 1881, Prodromus, p. 467.
Definition.—Dorataspida without perforated plates; shell composed only of the meeting branches of the two opposite apophyses, which arise from each radial spine. Condyles of the branch-ends without by-spines.
The genus Phractaspis is the most simple and primitive form among all Dorataspida, and may be regarded as the common ancestral form either of this whole family, or at least of its first subfamily, the Diporaspida. In all members of this subfamily the spherical shell is composed of twenty radial spines, each of which bears two opposite apophyses; but the mode of composition is different in the two tribes of the subfamily, in the Phractaspida and Ceriaspida. In the simpler tribe, the Phractaspida, the shell is composed only of the meeting branches of the apophyses of neighbouring spines; there are no peculiar perforated plates or shields. In the Ceriaspida, however, both apophyses of each single spine form a perforated plate or shield by union of their branches, and the shell is formed of the meeting edges of these shields. Of course the Ceriaspida must be derived from the simpler Phractaspida. Phractaspis, as the common ancestral form of both, exhibits a very simple structure of the shell (Pl. [137], figs. 1, 2). Commonly, if the fork-branches of each apophysis be not again branched, the shell possesses only twenty-two large meshes and forty sutures. More rarely their number increases, the fork-branches of the apophyses being again branched (Phractaspidium, Pl. [137], fig. 3).