BAILY — ON MARINE INVERTEBRATA AX PORTMAB.NOCK. 255 



it is often thrown ashore in large quantities. I did not myself find it to 

 be nearly so abundant as Uraster rubens. 



Echinus sphara, the common Egg Urchin, or Sea Egg. — I observed 

 one specimen of this abundant species, which, according to Forbes, is 

 found on ail the shores of Britain and Ireland. 



Spatangus purpureus, Purple Heart Urchin. — I found a fragment 

 only of this species, having the large spines attached. It is said to be 

 rare in Ireland, being found on the coast of Wicklow, but is abundant 

 on the Scallop Banks of the Isle of Man. 



Amphidotus cordatus — Common Heart Urchin, or Mermaid's Head— 

 This, the commonest of all heart urchins, Eorbes describes as abounding 

 in all our sandy bays, and says that often after storms great numbers 

 are cast ashore ; these remarks are quite borne out as to the quantity 

 strewn upon the beach at Portmarnock; if anything, they were still 

 more plentiful on the coast at Aberdeen, as I observed whilst on a visit 

 there some years ago, it being difficult to step without crushing some of 

 them. 



ANNELIDA. 



The tubes of Terelella, which are constructed of sand and small 

 shell fragments, I found occasionally covering the shore in great num- 

 bers. 



Serpula vermicularis, S. triquetra, and probably other species, at 

 present undetermined, were found attached to stones, shells, and co- 

 rallines. 



Spirorbis communis. — The very small, white, coiled tubes, resem- 

 bling a miniature Nautilus, of this very common little Annelid occur 

 frequently upon the fronds of some of the larger seaweeds and co- 

 rallines. 



Aphrodita aculeata, Prickly Sea Mouse. — This remarkable animal 

 was found to be not uncommon, and several specimens were collected 

 alive ; the brilliant prismatic colours of its setse, and its large size, ren- 

 dering it a very conspicuous object. 



Nereis margaritacea, Hairy Bait. — This small and elongated form of 

 Annelid was found to be a frequent companion of the common Hermit 

 Crab, sharing with it its stolen shell. This curious association of two 

 animals so distinct has been alluded to by Mr. Gosse and others. 



CRUSTACEA. 



Sub-class CiERirEDiA. Balanidce, or Barnacles. 



Balanus porcatus. — I found a large specimen of this species on the 

 valves of Pecten opercularis (dead), and the same species (living) on 

 various other shells. 



B. communis is an abundant species at this locality (living), on rocks 

 and shells. 



