222 Mr. E. Forbes on a Shell-bank in the Irish Sea, 



but during the last three years I have only taken as many 

 specimens. 



Animals of the class Kchinodcnnata arc abundant. Star- 

 fish of the family AjBteriae abound on the bank, those of the 

 family Ophiurae on its edge. Among gravel Echinus suban- 

 gularis is common : among the scallops Echinus esculenius. 

 Spatangus cordatua is very rare, while Sp. purpureas is very 

 common, as also Echinocyamus pusillus. Holothurice are ex- 

 tremely scarce, two species only having been found, and but 

 one specimen of each. 



Among the zoophytes, of late Plumularia myriophyllum has 

 become common ; and this year I have taken twenty speci- 

 mens of the rare Thuiaria articulata, which I never observed 

 in our sea before. Every dredging excursion I make I add to 

 our local list of zoophytes and naked mollusca, but seldom 

 now find a testaceous mollusk new to the district. The inha- 

 bitants of this bank belonging to the classes Mollusca, Echi- 

 nodermata and Zoophytes, may be summed up as follows : 



Mollusca Univalve Testacea 27 



Bivalve Testacea 44 



Nudibranchia 9 



Naked Acephala 4 



84 



Echinodermata . . Asteriadae 14 



Echinidae 5 



Holothuriadas , 2 



21 



Zoophytes Hydroiada 11 



Asteroida 1 



Helianthoida . . , 2 



Ascidioida 14 



28 



I shall now, before concluding, notice a few points wherein 



this review of the Ballaugh scallop-bank may be made to 



bear on Geology. 



Supposing the bank converted into a fossil bed similar to 

 the shell-marls of the Pleistocene or newer Pliocene aera, let us 

 see what effect such change would have on the Fauna. 



1. We should be able to form a pretty accurate idea of the 

 testaceous mollusca inhabiting it, but not of the naked mol- 

 lusca, as the latter would wholly disappear. 



