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Show 180 PROF. F. JEFFREY BELL ON THE [Mar. 1, ossicles articulate with one another by means of a more or less simple ball-and-socket joint; the covering plates are more or less regularly developed as superior, inferior, and two lateral, the last of which bear spines. The Astrophiuree (s. Cladophiurae) are Ophiurids in which the ambulacral ossicles articulate with one another by means of hourglass- shaped surfaces, and are covered by granular deposits in the thick integument; the arms may be simple or branched repeatedly. The Zygophiurae are Ophiurids in which the movement of the ossicles on one another is limited by the development of lateral processes and pits ; superior, inferior, and lateral spine-bearing plates are always developed as a covering for the arms, which are always simple, and incapable of coiling round straight rods. The Streptophiuree. The following facts justify the vagueness of the definition offered. a. Upper arm-plates: absent in Ophiomyxa vivipara, double in O. pentagona, of several pieces in O. flaccida; double in Ophioteresis; in Hemieuryale a mosaic of small plates; single but incomplete in Neoplax. ft. Under arm-plate: absent from Ophioteresis, alone among existing Ophiurae. y. Tentacle-scales: absent from Ophiomyxa, Neoplax, and Ophiobyrsa. 1. Tooth-papillce: absent from Sigsbeia, Hemieuryale, Ophiochon-drus, and Ophiomyxa. e. Radial shields are small and short in Ophiobyrsa, small and irregular in Ophiomyxa, rather large in Ophioteresis, large in Hemieuryale, and very large in Sigsbeia ; on the other hand, they are absent from Neoplax. The order in which the genera just mentioned should stand to one another is a question which cannot be discussed now, nor can that of the relation, clearly enough marked in many points, between the Streptophiurae and the lowest of the Zygophiurae : the "articulating peg " in Ophioscolex is described as minute; it, Ophiambix, Ophio-sciasma*, Ophiogeron*, Ophiohelus*, and Ophiotholia have no upper arm-plates, while in Ophiomyces they are, if present, minute ; in the three genera marked with an asterisk the arm-ossicles retain the embryonic character of being nearly divided into two. In addition to the genera placed under the " Astrophyton-like Ophiurans " of Mr. Lyman-Ophiobyrsa, Ophiomyxa, Ophiochon-drus, Hemieuryale, and Siysbeia-to which, of course, must he added Neoplax, I would place in the Streptophiurae the genera Ophiomyces, Ophiotholia, Ophiohelus, Ophiosciasma, Ophiambix, and Ophioscolex. Mr. Lyman says of Ophioblenna, which he places next to Ophioscolex, " Of its skeleton I am quite ignorant." I applied, therefore, to Dr. Liitken, who has charge of the only known specimens, and he |
