ECHINUS. 149 
The longest primary spines of specimens of this size vary from 
8-4 to 4 mm. 
Distribution. Both sides of North Atlantic, from Norway to 
Valentia, and Halifax, U.S., to Florida; off Japan; off Patagonia. 
Littoral to 2435 fms. 
a. Zetland. R. M‘Andrew, Esq. 
b-k. 52° 25' N., 11° 40’ W., 80-110 fms. ‘ a ate ? Exp. 
I,m. 50° 29’ 26" N., 11° 4° W., 400 fms. G. C. Bourne, Esq. 
3. Echinus microstoma. (Plate XIV. figs. 1 & 2.) 
Echinus microstoma, Wyv. Thoms. Phil. Trans. clxiv. (1874) p. 744, 
pl. Ixviii. figs. 1-10; Norman, Ann. § Mag. vi. (1880) p. 455; Bell, 
Ann. § Mag. iv. (1889) p. 440, pl. xix. fig. 1. 
Primary spines not numerous, of moderate length, fairly stout, 
taper very gradually or end bluntly; white, straw-coloured, or 
crimson ; shorter, blunter, and more closely packed above than 
below the ambitus; rather finely striated. Secondary spines very 
fine and rather sparse above the ambitus, below which they are 
stouter and more numerous. Pedicellariz not abundant. 
Test very thin, somewhat flattened above, tumid below; small 
peristome, a little depressed ; calycinal area of moderate size; both 
primary and secondary tubercles rather rare above the ambitus, but 
much more numerous below. Calycinal area with rather large peri- 
proct, from which all the radials are shut off; madreporite not very 
prominent; the tubercles on the interradials are confined to the inner 
half, where they are closely packed. In the interambulacra there are 
about twenty plates, each with a prominent central primary tubercle ; 
these diminish in size more markedly as they approach the peri- 
stome than the periproct, above the ambitus they are surrounded 
by a few secondary and miliary tubercles, which are more numerous 
and definitely arranged below it. There are rather less than thirty 
compound pore-plates; these bear distinct primary tubercles at and 
below the ambitus only ; above it only an occasional plate here and 
there carries a largish tubercle. The number of smaller tubercles 
is also scanty above, and not very large below the ambitus. The 
peristome is small and depressed, and the gill-cuts are not well 
marked. The surface of the test is a brilliant brick- or salmon-red, 
with which a little yellow is sometimes combined. 
The bright-red colour, the thin test, and the proportionately small 
peristome easily distinguish this species, which is very common in 
deep water. Its range of variation does not seem to be as marked 
as that of some other members of the genus. 
Diam. of test. Height. Peristome. Periproct. 
68 34 Mi 14 
a0 25 12 Ss) 
47 20 13 3) 
43 19°5 115 3) 
40 21 10°5 4°5 
