334 ECHINODERMS OF THE BRITISH ISLES 



distinguished with full certainty by means of their triphyllous 

 pedicellariae already in the quite young stages before the specific 

 characters of the test have appeared, the triphyllous pedicellariae 

 appearing very soon after metamorphosis and as the first of all 

 the pedicellariae. 



A small Amphipod, Urothoe marina Sp. Bate, lives as a 

 commensal with this sea-urchin in its hole. 



In British seas this species is very common all round the 

 coasts. It is mainly a littoral form, and may in several places be 

 dug up from the sand at low tide. Its distribution elsewhere is 

 very wide, cosmopolitan, the forms living at S. Africa, Australia, 

 New Zealand, Japan, etc. being scarcely distinguishable from the 

 European form. In the European seas it occurs from Tromso to 

 the Sound on the Scandinavian coasts, and from the British seas 

 to the Mediterranean. It is, however, not knowTi from Iceland 

 or Greenland. Bathymetrical distribution, 0-ca. 230 m. 



2. Echinocardium flavescens (O. Fr. Miiller). (Fig. 194, 3.) 



(S3ni. Echinocardium ovatum Gray ; Amphidetus ovatus 

 (Leske) ; Amph. roseus Forbes.) 



Frontal ambulacrum not sunk, the anterior end of test rounded 

 or at most wdth a very slight notch. Pores of frontal ambulacrum 

 within the fasciole distant, in regular single series. Test not 

 sloping anteriorly, almost vertical before the fasciole ; the 

 greatest height usually at the anterior edge of the fasciole. A 

 variable number of larger tubercles (spines) ^ in the paired inter- 

 ambulacra above the ambitus. Labrum somew^hat prolonged 

 backwards, reaching to the middle of the adjoining second am- 

 bulacral plates (Fig. 196, 2). The globiferous pedicellarias 

 (Fig. 195, 3), which are usually fairly numerous and conspicuous, 

 darkly pigmented or yellow, have a slender stalk, without free 

 projecting rods ; the valves usually have 6-8 long, slender teeth 

 at the terminal opening ; the tridentate pedicellarise (Fig. 195, 4) 

 are in the main like those of cordatum, the triphyllous (Fig. 197, 2) 

 have the edge of valves nearly smooth, with only a few serrations 

 at the base. Colour in life yellow or rose. Reaches scarcely as 

 large a size as the preceding species. 



The biology of this species has not been closely studied, but 

 very probably it is like that of Ech. cordatum, although it 



1 It is sometimes very difficult to distinguish these larger spines ; on 

 denuding the test of such specimens one may find the grooves in which the 

 larger spines have been attached, the spines liaving for some reason or 

 other been lost and replaced by new, much smaller spines. 



