REVISION OF PALEOZOIC STELLEROIDEA. 



213 



Subclass AULUROIDEA. 



Auluroidea SCHONDORF, Palaeontographica, vol. 67, 1910, p. 60; Jahrb. nassauisch. 



Ver. Naturk., Wiesbaden, vol. 63, 1910, pp. 234, 247, 251. SPENCER, Mon. 



Brit. Pal. Asterozoa, pt. 1 (Palseontogr. 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 

 sharply marked off from the disk as 

 appendages. This means that the 

 body cavity does not extend from 

 the disk into the rays as in Aster- 

 oidea. On the actinal side the rays 

 have open ambulacral furrows with 

 the ambulacralia never anchylosed 

 into vertebrae ; they are arranged in 

 two columns, the pieces of which 

 are either alternate or opposite one 

 another. 



Original definition. "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 hollo wed-out 

 body, which, as the plates of the two columns 

 are normally united, forms the medial ambu- 

 lacral canal; and of a lateral process extend- 

 ing to the adambulacrals, with depressions 

 on both sides of it in the ventral surfaces of 

 the ambulacrals and adambulacrals [see fig. 

 14]. [These large lateral depressions are not podial openings through 

 or between the plates as in asterids, but appear to be cavities for the 

 ampullae or for these and podial insertions. Dorsally the ambulacrals 



FlG. 12. A SECTION THROUGH THE ABM OF AN 

 ASTEKID, AFTEK SCHONDORF. A , AMBULACRA- 

 LIA; Ad, AD AMBULACRALIA; Amp, AMPULLA; 

 D, DORSAL SKELETON; F, PODIA; ipl, ACCES- 

 SORY OSSICLES; Mo, ATTACHMENT FOR UPPER 



LONGITUDINAL MUSCLES; Mo 1 , UPPER TRANS- 

 VERSE MUSCLE ; Mu, ATTACHMENT FOR LOWER 

 LONGITUDINAL MUSCLE; Mv>, LOWER TRANS- 

 VERSE MUSCLE; Mv, VERTICAL MUSCLE ; Bo, 

 UPPER MARGINALIA; Ru, LOWER MARGINALIA; 



Wr, RADIAL WATER- VESSEL. 



FlG. 13. A SECTION THROUGH THE 

 ARM OF A TRUE OPHIURID, AFTER 

 SCHONDORF. Bs, VENTRAL SHIELD; 



C^CUTIS; F, PODIA; L, BODY CAV- 

 ITY; N, NERVE-RING; oZm, uZm, 



UPPER AND LOWER INTERMEDIARY 

 VERTEBRAL MUSCLES; Rs, DORSAL 



SHIELD; Ss, LATERAL SHIELD; W, 



VERTEBRA; Wr, RADIAL WATER- 

 VESSEL. 



