Th. Mortensen: On the alleged primitive Ophiuroid, Ophioteresis elegans Bell. 5 



deductions, and it is highly improbable that it occurs at all. Il is much more 

 probable the ambulacral vessels and nerve trunks pass in Ophioteresis through the 

 aperture in the centre of the vertebral ossicle which Gregory figures plainly enough 

 (Fig. XIV), while maintaining a discreet silence about it". It is true that Bell 

 does not say anything about the existence of an open ambulacral furrow in Ophio- 

 teresis ; but the faet that Bell states that *'on the middle line of thcir (the arms) 

 lower surface there is a distinct groove" (Op. cit, p. 178) combined with his emphasis 

 of the primitive character of Ophioteresis and his mentioning Tæniaster and Protaster 

 in connection with it would seem thus far to justify Gregory's conclusion^) and, 

 moreover, Bell does not say a word either of the aperture in the vertebræ. 



Ever sincc the beginning of my studies on Echinoderms I have been looking 

 for an opportunity of studying more closely this remarkable Ophiurid. I have 

 never felt convinced of the correctness of Bell's observations on its structural 

 features ; indeed, I think, it will be agreed that a figure like PI. XI, 4, reproduced 

 in text figure 1 (p. 8), is anything but convincing ; and if there is really no ventral 

 plate, what does then the aperture in the middle of the vertebra mean ? For if it re- 

 presents the ambulacral furrow, closed by thick skin, this must evidently be an 

 important argument against its primitive character; it would simply mean that the 

 absence of the ventral piates was a secondarily acquired feature. On the other 

 hånd, if the observations of Bell prove to be correct, it would evidently be of 

 quite unusual interest to study the anatomy of such a remarkable form, since 

 Bell has left us in total ignorance of this side of the question. 



On going over recently a collection of zoological material made by Captain 

 E. SuENSON in the San Bernardino Strait, Philippines, I found some specimens of 

 a small Ophiuran , which at once aroused my interest ; the faet that no ventral 

 piates could be seen, and that the side arm piates were almost at a right angle tu 

 the arm, recalled Ophioteresis, so that I thought at first I had another species of 

 that genus before me. On dissolving a piece of an arm in Eau de Javelle, I found 

 liowevor, that it really had ventral piates, but these are completely obscured by 

 the thick skin. As this is also the case in Ophiothela, with which genus this species 

 also agrces in the covering of the disk and the dorsal side of the arm, and as also the 

 side plates in Ophiothela stand out from the arm, it is plain enough that it belongs 

 to this genus, representing a new species. It is a five-armed form, without the faculty 

 of self-division, all the other species having 6 arm« and being self-dividing, except 

 unc species, Ophiothela tigris Lyman, which difTers, however, so much from the new 

 form, that the idea of their identity must at once be abandoned. 



') On p. 288 in the "Treati«e on Zoology" III. Orecory says: "in the living OphioUntu 

 there are no ventral piates, and a shallow ambulacral furrow is accordingly present". 



