186 
need no detailed description; reference to the figures given here 
(PI vi II, Figs. 12—13) and to Clark's description will suffice. 
The ophicephalous pedicellariæ are generally very long-stalked; the 
cross-piece at the tip of the loop of the largest valve may some- 
times be well developed, but as a rule it is not developed, as stated 
by Clark. The head is sometimes invested in a rather thick pel- 
lucid skin. (Preservation may have something to do with this feature) 
The triphyllous pedicellariæ are described and figured by Clark 
as wide and flat, with the blade simply oval. This is, evidentlv. 
due to a mistake; probably it is a pedicellaria of another Echinotd, 
accidentally lying aniong the spines of Echinobrissus, which Clark 
has struck upon; such a thing is by no means a rare occurrence 
(comp. above, sub. Heliocidaris tuberculata, p. 175). The triphyllous 
pedicellariæ of Echinobrissus are of quite another, rather unique 
shape, although easily referable to the usual shape of this type of 
pedicellariæ (PI. VIII, Fig. 11). The blade makes a sharp fold in 
the middle so as to form a distinet keel, reaching almost down to 
the apophysis. The edge of the blade is rather coarsely serrate, 
the serration continuing along the keel. The sphændiæ are quite 
smooth, the stalk very distinetly set off; they are attached in fairly 
deep grooves, but not concealed. In adult specimens they are found 
in the number of 5—6, attached close to each tubefoot of the inner 
series, thus forming two longitudinal series in each ambulaerum. 
The spicules of the tubefeet are peculiar, straight, smooth rods 
with rounded ends and a small, rounded median prominence. They 
are very regularly arranged, lying obliquely, in two rows, all with 
the processes turning outwards. The sucking disk is provided with 
a fairly well developed calcareous ring, consisting of 4—5 some- 
what irregular parts (PI. VIII, Figs. 10, 14). The ambucral giils 
contain a few spicules of the same kind as those of the other feet; 
they even have a trace of a calcareous ring in the point. 
The spines are very smooth; the primary ones are simply tapering, 
the miliary spines distinetly widened at the point. (PI. VIII, Fig. 9). 
The young specimens in my material afford a most desirable op- 
portunity of studying the growth changes of this rare form. In the 
youngest specimens, only 5 mm long, the outline of the test is 
already the same as in the adult; but the peristome is in the middle 
of the oral side, while in the adult it is distinetly anterior. The 
