178 PROF. F. JEFFREY BELL ON THE [Mar. 1, 



legists 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 " Astrophyton-like Ophiurans " 

 make an attempt to acquire the saddle-shaped ossicle of the Astro- 

 phytidse ; 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 pro- 

 vided with teeth and tooth-papillse, but there are no mouth-papillse. 

 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 ex- 

 tremely generahzed condition which they present. As will be seen 

 from the drawings (figs. 4 and 5, Plate XI.), 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 



