. Bulletin - United States National Museum. Science. Subclass AULUROIDEA. Auluroidea Schondorf, Pakcontograpliica, vol. G7, 1910, p. 60; Jahrb. nassauisch. Ver. Naturk., Wiesbaden, vol. 63, 1910, pp. 234, 247, 251.—Spencer, Men. Brit. Pal. Asterozoa, pt. 1 (Paloeontogr. Soc. for 1913), 1914, pp. 24,48. Protophiuroidea and Euophiuroidea Sollas and Sollas, Philos. Trans. Roy. Soc. London, ser. B, vol. 202, 1912, pp. 214,222. Auluroidea are Paleozoic brittle-stars, with a more or less well- developed central disk, whose border between the rays is more often concave than convex; in other words, st
. Bulletin - United States National Museum. Science. Subclass AULUROIDEA. Auluroidea Schondorf, Pakcontograpliica, vol. G7, 1910, p. 60; Jahrb. nassauisch. Ver. Naturk., Wiesbaden, vol. 63, 1910, pp. 234, 247, 251.—Spencer, Men. Brit. Pal. Asterozoa, pt. 1 (Paloeontogr. Soc. for 1913), 1914, pp. 24,48. Protophiuroidea and Euophiuroidea Sollas and Sollas, Philos. Trans. Roy. Soc. London, ser. B, vol. 202, 1912, pp. 214,222. Auluroidea are Paleozoic brittle-stars, with a more or less well- developed central disk, whose border between the rays is more often concave than convex; in other words, star-shaped. The rays appear al- ways to be five in number, simple, long and slender, and more or less sharpl}^ marked off from the disk as appendages. This means that the body cavity does not extend from the disk into the rajs as in Aster- oidea. On the actinal side the rays have open ambulacral furrows with the ambulacralia never anch3dosed into vertebrae; they are arranged in two columns, the pieces of which are either alternate or opposite one another. Onglnal deiinition.—"The ambu- lacral water-vascular system lies in a circular canal that is situated wholly within the ambulacralia medi- ally between the adjoining columns of ossicles. From it diverge short side branches that either partially penetrate the substance of the individual ambulacrals, or lie in the suture between adjoining ambulacrals; in either case they extend into the ventrally open, broad ambulacral furrow. Ambulacrals free, not coossified, those of adjoining columns either alternate or opposite, but always di- rectly opposite the adambulacrals. Ambu- lacrals ventrally composed of a medially situated, internally concavely hollowed-out body, which, as the plates of the two columns are normally imited, forms the medial ambu- lacral canal; and of a lateral process extend- mg to the adambulacrals, with depressions on both sides of it in tlie ventral surfaces of the ambulacrals and adambulacrals [see fig.
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