OPHIUBANS OF UNITED STATES NATIONAL MUSEUM. 69 



A. nisei are very large and they have been exactly figured by Liitken, but I observe 

 that, on the margin of the disk, the plates which are succeeded by those of the 

 under face have a tendency to stick up as they do in the genus OpTiiophragmus, 

 and some of them even elongate to some extent, an arrangement which tends to 

 form a transition toward that which we see in A. erecta, where there are actual 

 spines; I even find in the A. riisei specimen, at about the middle of one of the 

 interradii, two very distinct little spines which are visible only from the Ophiuran's 

 under face. The mouth shields are a little narrower and more elongated than is 

 shown in Liitken's drawing, where the adoral plates are short and fairly thick; 

 a shape which is consequently altogether different from the one we see in A. erecta. 

 The first brachial under plate is broadly widened, and wider than in A. erecta, a shape 

 which corresponds to the shortness of the adoral plates. 



Lxitken has not mentioned the special character displayed on his specimen 

 by the second brachial spine of the first eight or nine articles, that is to say, up to 

 or a little beyond the margin of the disk ; each of these conical spines bear at their 

 obtuse end a crown of very short little spinules, which are conical and with rounded 

 points ; this crown progressively disappears and is no more visible beyond the disk. 

 I give here a photograph of the under face of the specimen from the Copenhagen 

 Museum (pi. 6, fig. 3). 



A. atra (Stimpson) is also very near A. erecta; it differs from it, as does A. riisei, 

 in having wider mouth shields, smaller brachial spines, separated under brachial 

 plates, wider adoral plates, and no spines on the disk. 1 



AMPHIODIA (=AMPHIURA) LttTKENI (Ljungman). 



Plate 6, figs. 1-2. 

 Amphipholis lutkeni LJUNGMAN (71), p. 631. 



When describing, above, AmpJiiura erecta, I referred to A. lutkeni because 

 it also has spines at the margin of the disk. We know that A. lutkeni has been 

 described by Ljungman from a single specimen found at Tortola, at a depth of 

 10 fathoms. Having had the opportunity to examine Ljungman's original specimen, 

 which was most kindly lent me by Professor Th6el, I can add a few additional facts 

 to Ljungman's description, and I also reproduce two illustrations representing 

 the upper and under faces of this species, which does not appear to have been either 

 seen or mentioned since 1871. 



The disk is 6 mm. in diameter. The arms are extremely long; their length 

 can not be exactly measured because they are more or less twisted, but they certainly 

 exceed 80 mm. 



The disk is pentagonal, slightly excavated in the interradial spaces ; its outline 

 is somewhat irregular in the single specimen which I have in hand. The upper face 

 is covered with small, subequal, thin, and imbricated plates, among which no 

 primary plates can be distinguished; they become a little stronger near the radial 

 shields and near the margin of the disk in the interradial spaces. On this same 

 margin are seen a certain number of fairly strong, elongated, conical, and pointed 

 spines which are sometimes bent; there are also about 10 such spines in each inter- 



i While this memoir was passing through the press I received from the United States National Museum three specimens of 

 A . riiiei in a rather bad state; the words on the label were almost erased and I am unable to indicate their origin. 



