Th. Mortensen: On the alleged primitive Ophiurid, Ophioteresis elegaus Bell. 17 



During the visit to London I was informed by Prof. Mac Bride that Miss 

 J. Sollas had quite recently published a paper on Onychaster^), in which she had 

 made some observations on the structure of Ophioteresis. On my application Miss 

 Sollas kindly sent me a copy of the paper, so that I am able to mention it in 

 this additional note. 



Miss Sollas, who has had material of Ophioteresis from the British Museum, 

 besides a specimen from Cargados Carajas, an island N. E. of Mauritius, for study, 

 has made sections of the arms and found that the radial nerve and water vessel 

 have the position typical in Ophiurids. It is stated that dorsal piates are completely 

 absent, and that the vertebræ, of which photographs are given (PI. 9, fig. 2) „reveal 

 at once a general similarity to those of typical Zygophiurids and a close examination 

 shows that this resemblance is more than superficial" (p. 57). A detailed and careful 

 description of the articulating surfaces is given, from which the following conclusion 

 is drawn : „It seems then that justification for separating Ophioteresis from the Zyg- 

 ophiuræ is not to be found in the nature of the articulation, and the genus must 

 be removed from the Streptophiuræ as defined by Bell". A suture has been traced 

 „which marks off the median ventral region of the vertebra, suggesting that a separate 

 piece, hexagonal in outline and apposed to the ventral surface of the ossicle, has 

 become fused with it and has formed a floor to the radial canal ... It can hardly 

 be doubted that this hexagonal piece represents a ventral plate which has sunk in- 

 wards and merged its individuality in that of the vertebra". Also the glassy knobs 

 on the dorsal side of the vertebræ have been observed. 



After having found that „the vertebral articulation of Ophioteresis does not diffcr 

 in any marked way from the Zygophiurid type", Miss Sollas examined some other 

 more typical members of the Streptophiuræ, viz. Ophiomyxa vivipara and O, australis, 

 and found that they likewise „possess the essential characters of the Zygophiurid 

 ossicle". The conclusion is drawn that „if the group Streptophiuræ is to stand it 

 cannot be defined by the character of its vertebral ossicles" (p. 58). 



It is seen that the results of Miss Sollas's examination of Ophioteresis are fuiiy 

 borne out by my researches, some points being only more definitely settled by me, 

 e. g. that there is really a separate ventral plate, and that the division of the simplo- 

 armed Ophiurids into Zygophiuræ and Stroptophiuræ must be definitely droppe<l, 

 being supported by no facts whatever. 



It is rather curious that this fonn, which was thought to be of so great import- 

 ance in the study of the morphology and classiftcation of Ophiurids, bas now almost 

 at the same time been shown, as a result of two entirely independent researches, to 



') Igerna B. J. Sollas. On Onychaster, a Carboniferoos BritUe-8tar. I'hilos. Traiuaci. Ser. 

 U. Vol. 204. (Publ. Mparataly, May 15, 1918). — My pipw was sent to prim lun. 2. 



8 



