A Structural Feature, hitherto unknowk among Echinodermata, fouzstd in 



DEEP-SEA OpHIURANS. By ThEODORE LyMAN. 



Long after the main collection of the " Challenger " expedition had arrived, there were 

 sent me several glass slides containing additional specimens of Ophiuridae. One of these, 

 hastily examined with a weak lens, I labelled Ophiomyces, and set aside for further study. 

 In the very last cast made by Mr. Alexander Agassiz, during the "Blake" expedition of 

 1878-79, near the Barbadoes, and in 82 fathoms, there came up a small soft Ophiuran, 

 which seemed, under the microscope, to have little tufts resembling bunches of simple 

 hydroids on the sides of the arms. More careful search, with a higher power, showed that 

 these were bunches of minute spines, each enclosed in a thick skin-bag, and that they had 

 a most extraordinary form, resembling long-stemmed agarics, or parasols with small 

 shades. On going back to the " Challenger " Ophiomyces, this too exhibited the same 

 spines, and a third species, also brought back by the " Challenger," was found with sim- 

 ilar appendages. Their form, however, was not the most curious thing. It was by their 

 arrangement in two, or even three, parallel vertical rows, that they wholly differed from 

 all Ophiuridae hitherto known. For, with all the variety exhibited by the hundreds of 

 living species, there is not one that departs from the unvarying single row of articu- 

 lated spines. Not even the double rows of hook-bearing grains among the Astrophytidae 

 would be homologous, because these grains are not attached to the side arm-plates. In 

 one species, these parasol-spines stood' side by side with the normal arm-spines (Ophio- 

 tholia), while in the two others (Ophiolielus), they took the place of the normal spines. 

 Among known Echinodermata I have been able to find only a single instance of a some- 

 what similar spine, or pedicellaria. T.his is in Aceste bellidi/era Wyv. Thom., and is to be 

 figured in Mr. Alexander Agassiz' forthcoming work on the Echini of the " Challenger," 

 plate XL, fig. 66. The question whether these novel shapes are spines or pedicellariae is 

 not a very important one, since a pedicellaria is only a spine peculiarly modified. But 

 it may be said that their supplementary character and abnormal shape give these parasol 

 spines the position of what used to be carefully distinguished as pedicellariae. 



Ophiotholia is indeed an Ophiomyces with this peculiar character, while Ophiohelus is 

 an allied but distinct form. Both may be considered low genera, with elaborate appen- 

 dages. The want of radial shields and imperfect calcification suggest their position, 

 which is confirmed by the embryonic character of their arm-bones, Avhich are lono-i- 

 tudinally divided into the two halves they theoretically should have. These bones are so 

 large and independent, even close to the tip of the arm, that it is not easy to understand 

 how they can be spurs of the small side arm-plates, as they should be according to one 

 theory. Unfortunately I could nowhere find a terminal joint, which would have shown 

 how the arm-bones take their rise. 



