236 Prof. P. M. Duncan and Mr. W. P. Sladen on the 
The perignathic girdle is better preserved in some parts than 
in the specimen originally described by us; but while the 
pores of the ambulacra are not so clearly placed as in the 
early specimen, there are, beyond a doubt, sutures in the inter- 
radial expansions (the ridges). 
1. Taking the old and this new specimen as examples, it 
is shown in them that the interradio-ambulacral suture is 
distinct and that the pairs of pores are between it and the 
median suture of the ambulacrum. 
It appears, then, that no part of the expansions is truly 
ambulacral ; all is interradial. 
Very respectfully we would draw our friend’s attention to 
his drawing, fig. 2. There isa slightly oblique and not quite 
transverse suture separating the ambulacral plate of zone d 
nearest the peristome from the expansion. In our opinion 
that suture is the natural limit of the ambulacral region and 
is interradio-ambulacral. Consequently the plate which this 
suture bounds actinally is interradial and not ambulacral. 
2. As the evidence of the facts just noticed is clear and 
the drawing given by Prof. Lovén is doubtless correct, we 
must admit that variation is possible in the construction of 
the girdles of these forms, which are considered to be Gnatho- 
stomes by some and to be Edentates by other naturalists. 
3. In the specimen originally examined by us there is not 
the slightest vestige of sutures in any one of the expansions, 
‘and we had no right to assume that there were any. 
Prof. Lovén shows (op. cit. p. 9, fig. 1) that there are 
certainly three sutures in each expansion, irrespectively of 
what may be considered as interradio-ambulacral sutures. 
Possibly there are two others uniting small triangular pieces 
to the outer edges of expansions. 
In the lately cut specimen at the British Museum there are 
distinct sutures in the interradial expansions, but their distri- 
bution differs from that figured by Prof. Lovén. 
Prof. Lovén shows that in each expansion there is (a) a 
median suture, (8) asuture on either side of the median suture, 
being parallel at some distance. Each of these two sutures, 
which are parallel with the median one, bounds a plate at the 
side of the median suture which unites the plates. Hach one 
of these two sutures seems to start from close to the inter- 
radio-ambulacral suture at each branchial incision, a small 
space intervening. 
According to Prof. Lovén’s drawing (fig. 1) the interradio- 
ambulacral sutures are curved, and they limit a plate, a con- 
siderable part of which is free towards the ambulacrum and 
which has upon its corner the little plate and suture already 
