Though the number of Tuscarorida at present known is small (only three genera, with ten species), they represent a very distinct and remarkable family of Phæodaria, as well by their considerable size, as by the peculiar arrangement of the radial spines and the structure of the shell-wall, which in some species is more solid and thicker than in any other Radiolaria. The diameter of the shell is always more than 1 mm., usually between 1 and 2, and sometimes more than 3 mm.

The dry shell of the Tuscarorida is not hyaline and transparent as is usual in the other Radiolaria, but perfectly opaque, milk-white or yellowish-white. This opacity is caused by innumerable very fine pores, which everywhere pierce the thick, apparently solid, fundamental substance of the shell-wall. Besides those very small pores, it is also pierced by a certain number of larger pores, which are scattered at wide distances (Narr. Chall. Exp., vol. i. pl. A, fig. 15b). These larger pores or pore-channels have a diameter of about 0.01 mm., and pierce the shell-wall either in a perpendicular or in an oblique direction. Very numerous straight, simple, and thin needles, usually 0.1 to 0.2 mm. in length, similar to the thin tangential needles of the Aulacanthida, are everywhere scattered tangentially in the cement-like fundamental substance, which seems to be a peculiar carbonic silicate; their axis is parallel to the shell-surface.

The general form of the shell is somewhat different in the three genera of Tuscarorida; ovate or spherical in Tuscarora and Tuscarusa, which bear no caudal axial spine (Pl. [100], figs. 1-7), or sometimes three-sided pyramidal (fig. 4); it is spindle-shaped in Tuscaridium, which bears on the aboral pore an axial caudal spine (Pl. [100], fig. 8). In every case the main axis of the shell, determining its monaxonian fundamental form, is indicated by the mouth, which is placed in the oral pole of the main axis and prolonged into a short tube or proboscis.

The hollow apophyses, arising from the shell of the Tuscarorida, are always cylindrical, long and thin tubules, the narrow cavity of which communicates directly with the large shell-cavity. In the axis of the tubules lies a thin axial chord or funicle, composed of a few (usually three or four) siliceous threads which arise from bridges between the basal pores of the apophyses, and are twisted together like the strands of a rope. The axial funicle is connected with the thin wall of the tubular apophyses by innumerable very thin radial beams, perpendicular to the axis (Pl. [100], fig. 3a, 5b). The surface of the apophyses is almost constantly covered with numerous small bristles or spines, which are usually curved and directed towards their distal ends.

Tuscarora (Pl. [100], figs. 1-6) exhibits two different groups of apophyses, which may be distinguished according to their different position and direction as "circoral teeth" and "aboral feet"; the teeth immediately surround the opening of the mouth, whilst the feet are remote from it and usually placed in the aboral half of the body, more rarely in the equator or in the oral half. The general form and structure are the same in both groups of apophyses, but their position and direction is different; the circoral teeth are directed forwards, often parallel (at the base at least), while the aboral feet are either divergent and directed backwards, or they diverge forwards in the basal part, then form a large arch, and finally curve backwards.

The number of the aboral feet, and their position relative to the circoral teeth, are different but probably constant in each single species, and serve, in the first place, for the distinction of genera and species. Tuscarora (in restricted sense) (Pl. [100], figs. 1-6), has constantly three feet (comparable to the three cortinar feet of the tripodal Nassellaria); Tuscarusa (Pl. [100], fig. 7) has four feet, opposite in pairs and forming a regular cross; Tuscaridium, finally (Pl. [100], fig. 8), has only one foot, which is situated in the main axis, on its aboral pole, and may therefore be called a caudal spine.

The number of the circoral teeth varies from two to four, and is usually three. Originally these three teeth alternate regularly with the three aboral feet, so that the latter may be regarded as perradial, the former as interradial (Pl. [100], figs. 1-4). The proportion of the number of each group of apophyses in the different species is synoptically shown in the following table:—

Depth
in
Fathoms.		Challenger
Station.		Length
of the
Shell.		Breadth
of the
Shell.		Number
of Feet.		Number
of Pedal
Pores.		Number
of Teeth.		Number
of Dental
Pores.
1.Tuscarora bisternaria,30002642.01.53838
2.Tusc"roramurrayi,20002952.51.53333
3.Tusc"rorawyvillei,22502911.51.43434
4.Tusc"roratetrahedra,24503482.52.03433
5.Tusc"roratubulosa,30002491.41.23423
6.Tusc"roraporcellana,26503251.51.33424
7.Tusc"rorabelknapii,20252932.51.53342
8.Tuscarusa medusa,31252531.21.04422
9.Tuscaridium cygneum,30502503.21.61244
10.Tusca"idiumlithornithium,30002643.61.81446
a = Depth in Fathoms.
b = Challenger Station.
c = Length of the Shell.
d = Breadth of the Shell.
e = Number of Feet.
f = Number of Pedal Pores.
g = Number of Teeth.
h = Number of Dental Pores.
(a)(b)(c)(d)(e)(f)(g)(h)
1. Tuscarora bisternaria
30002642.01.53838
2. Tuscarora murrayi
20002952.51.53333
3. Tuscarora wyvillei
22502911.51.43434
4. Tuscarora tetrahedra
24503482.52.03433
5. Tuscarora tubulosa
30002491.41.23423
6. Tuscarora porcellana
26503251.51.33424
7. Tuscarora belknapii
20252932.51.53342
8. Tuscarusa medusa
31252531.21.04422
9. Tuscaridium cygneum
30502503.21.61244
10. Tuscaridium lithornithium
30002643.61.81446

The base of the apophyses in all Tuscarorida is inflated, conical, and pierced by a small number of large ovate pores, the typical "basal pores," which occur also in the closely allied Circoporida. The number of these basal pores varies from two to eight, and is usually three or four; it never becomes in this family so great as in the Circoporida, where each circle of pores is often composed of sixteen to twenty-four or more basal pores. The number seems to be rather constant in each single species, as may be seen in the preceding Table. The pedal pores (on the base of the aboral feet) are usually larger than the dental pores (on the base of the circoral teeth). Their form is usually irregularly ovate or triangular; their outer aperture is armed with spines or bristles, which are commonly larger than in the other parts of the apophyses.