The family Stephanida is the most simple of all Stephoidea, and probably the common ancestral group of this suborder (compare above, p. [933]). The skeleton consists of a simple ring only, surrounding the central capsule, and armed commonly with simple thorns or with larger branched spines. The branches of these spines are constantly free, never joining together. Therefore the shell exhibits no trace of fenestration or lattice-work, no pores or gates, except the simple large gate of the ring itself. In all other Stephoidea we find secondary gates or lattice-work.
The first known form of this family is Lithocircus annularis, described by Johannes Müller in 1858 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1). He observed already the central capsule ("Blase") surrounded by the circular ring of silex, and the calymma ("Strahlige Gallert") enveloping the whole body. The peculiar structure of the soft body, particularly the "area porosa" on the basal pole of the central capsule, and the pseudopodial cone within it, were first accurately described by Hertwig (in 1879). A great number of simple rings, similar to these, were found in the Challenger collection, and are here arranged in six genera and forty-eight species.
The simple ring of silex, which alone forms the skeleton of the Stephanida, corresponds to the primary or sagittal ring of the other Stephoidea, and lies therefore vertically in the median or sagittal plane of the body. We can therefore distinguish on it four different segments, rods or bows, two of which are more horizontal, two more vertical. The former are one upper bow or apical rod, and one lower bow or basal rod. The latter are one posterior bow or dorsal rod, and one anterior bow or ventral rod. Sometimes each of these four component bows is distinguished by a corner-spine, or by a pair of divergent branches.
In the two simplest (and probably oldest) genera of Stephanida, in Archicircus and Lithocircus, the dorsal and ventral rods of the ring are equal and cannot be distinguished; therefore the fundamental form is here amphithect, diphragmatic, or biradial (the poles of the sagittal axis being equal). In the four other genera the dorsal rod is more straight (often vertical) and more or less different from the ventral, convexly curved rod; therefore the fundamental form is here dipleuric or bilateral, as in the greater number of all Nassellaria (the poles of the sagittal axis being unequal). The general form of the ring in this latter case is commonly obliquely ovate or nearly triangular, the basal pole being more pointed, the apical pole more rounded (Pl. [81]).
The rods or bows of the ring are either roundish or cylindrical (with circular or elliptical transverse section), or they are prismatic or angular (commonly with triangular transverse section). In the latter case one edge usually is prominent in the sagittal plane (on the convex outside of the ring), whilst two other edges diverge laterally on both sides of it. The inner or concave margin of the ring is commonly smooth.
The inner perimeter of the large gate, enclosed by the ring, is commonly rounded (elliptical or ovate), rarely angular. However, the outer perimeter of the ring is nearly always polygonal, with prominent corners, and usually from these arise thorns or branched spines which are regularly disposed. Regarding this disposition we may distinguish three cases: A, the spines lie in the sagittal plane and form a single row, arising from the median edge; B, the spines lie on both sides of the latter and form two parallel rows, arising from the two lateral edges; C, the spines represent a combination of A and B, and are disposed in three rows, two paired rows arising from the two lateral edges, and an odd middle row between them, arising from the median edge. The spines are simple, without branches, in Archicircus and Zygocircus; more or less branched in Lithocircus and Dendrocircus. The branches are often richly ramified or arborescent, and exhibit great variety in size, special form, and direction (compare Pl. [81]).
The number and disposition of the spines or groups of spines are usually constant, and may be employed in the further progress of our knowledge, to distinguish a number of genera and subgenera. Very commonly (perhaps in the majority of the Stephanida) we find six groups of spines, an apical group on the upper rod of the sagittal ring, a basal group on the lower rod (on the porochora of the central capsule), two ventral groups on the anterior rod, and two dorsal groups on the posterior rod. In other species we find four or eight groups instead of six, and sometimes a larger number.
The most important of these apophyses of the ring are the basal spines, arising from its basal pole, where the porochora of the central capsule rests upon it. They are often much larger and more branched than the other spines, and attain a peculiar morphological value in the small subfamily Cortinida. Here we find three or four regularly disposed "basal spines," which may be compared to the typical "basal feet" of the Cyrtellaria, appearing in the majority of Spyroidea and Cyrtoidea. Cortina, one of the most important Nassellaria, bears three typical divergent feet on the base of the simple ring, two paired anterior or "pectoral feet," and an odd posterior or "caudal foot." The latter appears as a direct basal prolongation of the dorsal rod of the ring, and is opposed to an upper prolongation of the same, which corresponds to the "apical horn" of the Cyrtellaria (Pl. [97], figs. 1-3). As already explained above, these three basal feet of Cortina possess the highest phylogenetic value, since they may also be compared with the three primary radial spines of the Plectoidea, and so connect the Cyrtellaria and the Plectellaria. Stephanium differs from Cortina in the possession of four basal feet, an odd anterior or "sternal foot" being added to the three typical feet of the latter (Pl. [92], figs. 20, 21). Some forms of Plectoidea (Plagoniscus, Plectaniscus, &c.) seem to be nearly related to these Cortinida, and may be easily transformed into them by development of a complete ring, embracing the central capsule. They seem to demonstrate the near affinity of all these triradiate Nassellaria (Pl. [91], figs. 4, 5, 9, 10).
Synopsis of the Genera of Stephanida.
I. Subfamily Lithocircida. No typical basal feet on the base of the ring (no cortinar feet). |  | Ring diphragmatic or amphithect; dorsal and ventral bow equal. |  | Ring smooth or thorny, without branched spines. | 401. Archicircus. |
| Ring armed with branched spines, | 402. Lithocircus. | ||||
| Ring dipleuric, bilateral; dorsal and ventral bow different. | | Ring smooth or thorny, without branched spines, | 403. Zygocircus. | ||
| Ring armed with branched spines. | 404. Dendrocircus. | ||||
II. Subfamily Cortinida. Three or four typical basal feet on the ring (cortinar feet). | | Three basal feet (and an apical horn). | One caudal and two lateral feet, | 405. Cortina. | |
| Four basal feet (and an apical horn). | Two sagittal and two lateral feet, | 406. Stephanium. |