. Bulletin - United States National Museum. Science. 214 BULLETIN UNITED STATES NATIONAL Fig. 14.—a section through the arm of an aulurid, "with alternating ambulacralia, after schon- dorf. a, ambuxacralia of the dorsal and ven- TRAL skeleton; ^1, VENTRAL EXTENSION OF THE AMBULACRALIA; A d, ADAMBULACRALLV = LATERAL SmELDS OF OPHIURIDS; F, PODIA, ON LEFT THE CANAL PASSES THROUGH THE PLATE, ON RIGHT THE PLATE IS DISSECTED DOWN TO THE CANAL; TKr, INTERSKELETAL RADIAL WATER-VESSEL. are covered with spines and tubercles.] Disk with concave, or con- vex (?) mai'gins, with or without ma
. Bulletin - United States National Museum. Science. 214 BULLETIN UNITED STATES NATIONAL Fig. 14.—a section through the arm of an aulurid, "with alternating ambulacralia, after schon- dorf. a, ambuxacralia of the dorsal and ven- TRAL skeleton; ^1, VENTRAL EXTENSION OF THE AMBULACRALIA; A d, ADAMBULACRALLV = LATERAL SmELDS OF OPHIURIDS; F, PODIA, ON LEFT THE CANAL PASSES THROUGH THE PLATE, ON RIGHT THE PLATE IS DISSECTED DOWN TO THE CANAL; TKr, INTERSKELETAL RADIAL WATER-VESSEL. are covered with spines and tubercles.] Disk with concave, or con- vex (?) mai'gins, with or without marginal ossicles. Wlien the latter are present, they never extend along the rays, but are whoUy re- stricted to the disk. The rays on both sides are margined by the adambulacrals. Ventrally the rays have broad open ambulacral fur- rows, bounded laterally by the adambulacrals. A typical mad- reporite [probably always] lies in one of the ventral interradii. "The group [subclass] is re- stricted to the older ; Remarks.—This subclass of Stelleroidea appears to be an in- dependent development whose structure partakes of that of the Asteroidea and the Ophiu- roidea, though more like the latter. The Auluroidea agree with the asterids in having open ambulacral furrows, and a true madreporite, which is, however, ven- trally situated, but otherwise the class is more like the ophiurids, smce the body cavity does not extend into the rays as in true starfishes. However, the water-vascular canal in the Auluroidea does not lie outside of the ambulacrals as in the Asteroidea, but within these ossicles along the mid-line of the ambulacrum m a canal that is cut out of the sides of adjoining ambulacral columns. On the. other hand, the Ophiu- roidea have the am- A6 A A t :> Ad ^ A Ad bulacralia coossified and modified into vertebral ossicles; there are no open ambulacral furrows, and the entire rays are covered by four columns of shields or by an integument more or loss s
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