ECHINUS. 153 
but not always, shut off from it ; three large tubercles often on inner 
edge of each interradial. In the interambulacra there may be as many 
as seventy plates, and on these a tendency may sometimes be observed 
to carry alternately one and two large primary tubercles ; there is 
typically a regular row of primary tubercles from pole to pole fringing 
the poriferous zone, but with increase of size several of them may 
become absorbed. ‘The tubercles are rather larger and more closely 
packed below than above the ambitus ; there are a moderate number 
of secondary and miliary tubercles. The number of compound ambu- 
lacral plates is about thirty, and they are covered by a number of 
primary tubercles, of which there may be as many as six in a 
rather irregular row ; there may be two irregular rows, and the 
irregularity may be further increased by absorption of some of the 
tubercles. No median bare space in either ambulacra or inter- 
ambulacra, except in rare cases. Peristome rounded or pentagonal, 
the membrane closely covered with plates bearing fine spines ; near 
the mouth the spines are much stouter, and a large number of 
pedicellariz are scattered among them. 
Distribution. East side of North Atlantic, North Sea, Mediter- 
ranean ; Port Nata] and John Adams Bank (Brazil). ‘To 110 fms. 
a. Loch Etive, 15-20 fms. John Murray, Esq. 
b. Tobermory, 30.fms. John Murray, Esq. 
c. 4 miles 8.E. of Sanda, 30-38 fms. John Murray, Esq. 
d,e. Between Sanda and Ailsa Craig, 24fms, John Murray, Esq. 
f-A. Wilbrennan Sound, 10-20 fms. Jobn Murray, Ksq. 
?,j. Loch Fyne, 80 fms. John Murray, Esq. 
k,l. Between Great Cumbrae and Wemyss John Murray, Esq. 
Ground. 
m. West coast of Scotland. 
n. Belfast Bay, 20 fms. Belfast Nat. Hist. & 
Phil. Soc. 
o. S.W. coast of Ireland, 50-GO fis. 
p. S.W. coast of Leland, 110 fms. 
q-t. ? Galway Bay. Royal Dublin Soe. 
u. Turbary, 8. Ireland. Dr. Grenfell. 
v, w. Off Liverpool. 
x, Fishing-ground off Lundy, 
y. Of Tenby. 
z. Off Tenby. Dr. Bowerbank. 
a’. Ulracombe, Dr. Gray. 
6’. Polperro. 
ce’. Falmouth. W. P. Cocks, Esq. 
d', Plymouth. C, Stewart, Esq. 
e'-h'. Plymouth, 
',7'. Poole, 24 fms., July 1889, F. J. B. Beckford, Esq. 
k'. Outside Portland Breakwater. Rev. 8. O. Ridley. 
l’. Herm, T. H. Powell, Esq. 
m'—p'. Fern Islands. W. Thorburn, Esq. 
q'-s'. Firth of Forth, Dr. Leach. 
t’. Firth of Forth. KE. Forbes, Esq. 
u'~7''. Montrose. W. Duncan, Esq. 
k'-m'’, Cromarty and Moray Firths. Dr. A. Sutherland. 
n'-w'', Moussa, Shetland. Ki. M. Nelson, Esq. 
