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Show 178 PROF. F. JEFFREY BEIX ON THE [Mar. 1, logists have no form known to them which gives any certain indication of Ophiurid affinities. The considerations which I have urged will perhaps induce the student to regard the streptospondyline type as earlier than the zygospondyline. I have now to show how that type is modified. Mr. Lyman has shown how the " Astrophy ton-like Ophiurans " make an attempt to acquire the saddle-shaped ossicle of the Astrophytidae ; we have among the several genera various modifications of the type which is seen at its simplest in Ophioteresis. 3. ACCOUNT OF OPHIOTERESIS ELEGANS. Among the specimens collected by Dr. Coppinger, of H.M.S. ' Alert/ while in the waters of the Western Indian Ocean, were some examples of a remarkable Ophiurid, the explanation of the structure of which was quite unattainable at the time when I was engaged in preparing a portion of the Report published by order of the Trustees of the British Museum, under the editorship of Dr. Giinther, F.R.S. Description of the General Appearance of a Specimen. This form is particularly elegant in appearance, owing to the green colour of the upper surface of the arms and the margins of the disk, and the ornamentation by light, wavy, meandering lines of the central portion of the disk with its dark background. Below, the colour is pale yellow, except in the interradial portions of the disk, which are dark, and marked by white wavy lines. The contour of the disk, which is of moderate size in proportion to the arms, is more or less distinctly pentagonal ; the regularity of the disk is, no doubt, due to the large size of the radial shields. These, however, are not apparent from the outer surface, for, like all the rest of the animal, they are enclosed in a thick softish skin. The oval slits are provided with teeth and tooth-papillae, but there are no mouth-papillae. The arms twist and coil on themselves ; at their sides the spines form mere papilliform projections, owing to the fact that their bases are encased in the thick investing skin ; on the middle line of their lower surface there is a distinct groove. Anatomical Details. Since the publication of Mr. Lyman's ' Challenger' Report, in which so many valuable figures were given of the characters of the ossicles of which the arms of various species of Ophiuroids are made up, every student of the group turns first to an examination of these parts of the skeleton. Those of Ophioteresis are particularly interesting from the extremely generalized condition which they present. As will be seen from the drawings (figs. 4 and 5, Plate X L ) , the recesses on the adoral side of the ossicle are excessively shallow, and, in correspondence with that, the articulating elevations on the aboral side are very slight and inconspicuous. But, at the same time, it is to be noted that |