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 

 Yalentia, and Halifax, U.S., to Florida ; off Japan ; off Patagonia. 

 Littoral to 2435 fms. 



a. Zetland. B,. W Andrew, Esq. 



b-k. 52° 25' N., 11° 40' W., 80-110 fms. ' Porcupine ' Exp. 



I, m. 50° 29' 26" N., 11° 4° W., 400 fins. G. C. Bourne, Esq. 



3. Echinus microstoma. (Plate XIY. figs. 1 & 2.) 



Echinus microstoma, Wyv. Thorns. Phil. Trans, clxiv. (1874) p. 744, 

 pi. lxviii. figs. 1-10 ; Norman, Ann. fy Mag. vi. (1880) p. 435 ; Bell, 

 Ann. $ Mag. iv. (1889) p. 440, pi. xix. tig. 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. Pedicellaria3 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 .. 14 



50 25 12 5 



47 20 13 5 



43 19-5 11-5 5 



40 21 10-5 45 



