354 On tJic Ecliinoidea or Sea-Urchins. [Sess. 



area of the Firtli of Forth. The first is the purple-tipped 

 egg-urchin {E. miliaris), always a small creature, and often 

 mistaken for the young of E. sphrera. It has a rose-coloured 

 body with white tubercles, and the primary spines are often 

 much longer than the others. The shell, when stripped of its 

 spines, presents a beautifully radiated appearance, on account 

 of the tubercles of the primary spines being so prominent. Its 

 madreporite is extremely porous, and its pedicellarife numerous 

 and peculiarly shaped. These features may always help to 

 distinguish it from E. sphsera. Our next genus is the green 

 pea-urchin {Echinocyamus pusillus), the smallest of all the egg- 

 urchins, and forming the link between the echini and spatangi, 

 having the dental apparatus of the former with the spines of 

 the latter. The specimens exhibited were recently taken from 

 the stomach of a haddock, in which out-of-the-way place I 

 have frequently found them. From amongst a heap of star- 

 fish remains and small shells there were picked out on this 

 particular occasion no fewer than fifty-five pea-urchins in a 

 perfect condition. Wlien alive, the colour of the shell is a 

 bright metallic green, which gradually becomes a dull white 

 after the death of the animal. Specimens of the pea-urchin 

 may often be found amongst the shell-sand on the beach, but 

 the creature is so tiny, and so like a small water-worn stone, 

 that it may easily be overlooked. 



The only other sea-urchin ordinarily found in the Firth of 

 Forth is the purple heart-urchin {Spatangxis purpitreus) — the 

 largest and handsomest of all our British spatangi. In this 

 class of sea-urchins there is no masticatory apparatus, and the 

 animal burrows by means of its spines amongst the sand, and 

 is also generally found to be filled with this unsavoury sub- 

 stance. The spines of the spatangus, as already said, are 

 well known to microscopists as lovely opaque objects ; but it 

 may not be generally known that amongst the sand of the 

 body-cavity there is frequently to be found a wealth of micro- 

 scopic material. These include minute crystals and portions 

 of quartz and felspar, which often polarise beautifully ; frag- 

 ments of shells ; numbers of sponge-spicules and foraminifera ; 

 and various well - preserved forms of diatoms. Without 

 knowing anything of the nature of this microscopist's treasury, 

 I lately examined the contents of several spatangi, and felt 



