| OCR Text |
Show 1040 DR. J. W. GREGORY ON THE CLASSIFICATION [Dec. 15, Bohm has founded the genus OpHopege on the type species of Aganaster [2 a. p. 159]. The genus Cholaster of Worthen and Miller [19. pp. 328-329, pl. xxxi. fig. 4] appears to be allied to Aganaster, but the structure of the ambulacral ossicles is unknown. Family 4. 0 N Y c H AS T E R ID ;E. Diaqnosis.-Streptophiurse with well-developed vertebral ossicles, and with very flexible, contorted, unbranched arms; there are no external arm-plates, the integument containing granules only. Distribution.-Keokuk and Burlington Stages, Lower Carboniferous, Iowa and Dlinois. Genus ONYCHASTER, Meek & Worth. Type species.-Onychaster flexllls, Meek & Worth. [Proc. Acad. Nat! Sci. Phil. 1869, p. 83; 11. pp. 526-528; 11 a. p. 510, pl. xvi. fig. 3]. Remarks.-This interesting genus has hitherto been placed among the Euryalidae, of which it has been regarded as the best known fossil representative. As Prof. Bell, however, has_ remarked, Meek and Worthen's clear figures of the vertebral ossicles show that the articular surfaces are Streptospondyline and not Cladiophiuroid. Family 5. EucLADiiDiE. Diagnosis. - Streptophiurae with contorted branching arms. There are five pairs of large plates (? radial shields') on the abacti-nal side. The madreporite is large ami dorsal in position. The arms have no external arm-plates, but are covered by a granular integument. Ambulacral ossicles primitively Streptospondyline. Genus EUCLADIA, H. Woodward, 1869'[18]. Type species.-Eucladia johnsoni, H. Woodward, Lower Ludlow, near Dudley. Remarks.-The affinities of this magnificent Starfish have been left in some doubt owing to the absence of information as to the structure of the vertebral ossicles. It has generally been assigned to the Euryalidae, owing to its granular integument and branching contorted arms. Fortunately, however, I have found the articular surface of the vertebral ossicles exposed on the side of the block of limestone containing the specimen. The articulation is truly Streptospondyline of a rather primitive type (fig. 6 a, b, p. 1041). The ossicle is egg-shaped in section, with the broader end above. Two broad muscle-fields occur, one at each of the quadrants of the ossicle. On the central line just above these there is a small knob. The upper half of the ossicle is occupied by two pairs of depressions separated by simple ridges. |
