A homogeneous crystalline deposit invests almost the whole of the minute spiral shell of a Calcarina, and sends out many cylindrical, but more generally club-shaped spines in all directions, though they usually affect more or less that of the equator, as in the typical form Calcarina calcar, which is exactly like the rowel of a spur. The spines are for the most part thick and clumsy, and give the shell a very uncouth appearance, especially when their extremities are forked. The turbinoid spire of the shell has a globose centre surrounded by about five whorls progressively increasing in size, and divided by perforated septa into chambers. Each whorl is merely applied to that preceding it, and does not invest it in the least degree. Internally the turns of the spire are separated from each other by the interposition of a solid layer of shell-substance quite distinct from the walls of the chambers. A crystalline deposit begins at the very centre of the spire in a thin layer gradually increasing in thickness as it proceeds, and sending off club-shaped spines from time to time so that the spines are of later and later production, and become thicker and longer. From this it is evident that the intermediate skeleton grows simultaneously with the turns of the spire, but strange as it may seem, their growth is independent, though both are nourished and increased by the sarcode in the interior of the chambers. For the intermediate skeleton is traversed in every part by an elongated network of canals, which begin from irregular lacunæ or openings in the walls of the chambers, and extend to the extremities of the spines. Through these canals threads of the sarcode body of the animal within the chambers have access to the exterior, and provide nourishment for the intermediate skeleton; while pseudopodia, passing into the water through pores in the last partition of the shell, provide for its growth and procure nourishment for the animal. The communication between the adjacent chambers in the whorls, is by means of a series of pores in the septa, or partitions; and it is through the pores of the last septum that the pseudopodia of the animal have access to the water to provide for the growth of the spire, for the punctures on the surface are merely the terminations of some of the branching canals. On approaching the surface the canals become crowded together in some parts, leaving columns of the shelly skeleton unoccupied which either appear as tubercles on the surface, or, if they do not rise so high, form circular spots surrounded by punctations which are the apertures of the canals.