12 Mindeskrift for J. Steenstrup. X. 



proof that the division of the Ophiurids into Zygophiuræ and Streptophiuræ cannot 

 be maintained. 



With regard to the vertebræ of Ophioteresis it should still be pointed out that 

 they show the peculiar feature of having on the dorsal side a number of glassy 

 knobs (PI. I. Fig. 8, PI. II. Fig. 4), arranged in two longitudinal series. They have 

 been observed by Lyman, as appears from his statement that "at the tapering end of 

 the arm there are still the two warts at the base of each joint (wrongly taken to 

 represent the dorsal piates), and between these a double row of fine grains". To- 

 wards the end of the arm they are, indeed, very conspicuous (in dried specimens), 

 but are also found in the grown part of the arm, only they are obscured by the thick 

 skin, which must be removed in order to make them distinct. This transformation 

 of part of the vertebræ into a glassy substance is a feature not known in other 

 Ophiurids (but occurring also in other species of Ophiothela), and would seem to 

 indicate a very specialized condition, contrary to Bell's supposition that the vertebræ 

 in this form are very primitive ; this supposition obtains no support from their 

 real structure. 



Regarding the anatomicai structure of the arms I can give no information 

 beyond the conclusions to be deduced from the study of the skeletal parts ; but 

 these are sufficient to show that there is full accordance with the typical arm- 

 structure of Ophiurids. Of the anatomy of the disk I can give no information at 

 all. It would, of course, have been very interesting to study the anatomy of this 

 form. But the high importance, which would have attached to the anatomy of 

 Ophioteresis^ if it had proved to be really so primitive, as it was supposed to be, 

 has gone. It may now be expected that its anatomy will pro ve to be very like 

 that of its nearest allies. Which are they? 



The mouth structure of Ophioteresis quite agrees with that of the Ophiotrichidæ, 

 and there is no character, which excludes it from that family. ♦ The thick skin 

 covering the ventral piates is found similarly in Ophiothela and Ophiopsammium, 

 the side arm-plates are as prominent in Ophiothela as in Ophioteresis ; the tentacles 

 issue from the side of the arm, not from the underside, in Ophiothela and 

 Ophiopsammium as well as in Ophioteresis; the naked skin covering the disk is 

 found alike in Ophiomaza and Ophiæthiops, as also in Ophiolophus, Gymnolophus 

 and Ophwhelix, where, however, the radial shields have a prominent crest. The 

 hook-shaped spines likewise are of general occurrence in the Ophiothrichidæ — in 

 short, no single feature can be pointed out by which Ophioteresis might be separated 

 from the Ophiothrichidæ. 



The genus of the Ophiothrichidæ to which Ophioteresis is nearest related, is 

 beyond doubt Ophiothela. Lyman was by no means very wrong in ref erring his 



