270 EDIBLE BRITISH MOLLUSCA. 



forms presented a most beautiful appearance, studding 

 the bottoms of the grey limestone rock pools."* 



At the Museum of the Jardin des Plantes, at Paris, 

 I have seen specimens of this Echinus in a block of 

 sandstone from the Baie de Douarnenez, in Finisterre ; 

 also, specimens of Echinus perforans in granite rock 

 from the Bay of Croisic. How these animals bore 

 into such hard substances is still a question ; it is 

 supposed by some that they first perforate with their 

 teeth and then soften the rocks by some secreted 

 solvent. f 



A friend of mine, who examined some of the holes, 

 observed that they are evidently formed by the animal, 

 and are lined with a smooth yellow substance which 

 it deposits on the stone; that in limestone rocks the 

 deposit is probably obtained from the stone itself by 

 means of a solvent, but that in granite it may be 

 derived from the lime held in solution in the sea- 

 water. 



Mr. H. N. Moseley mentions that at St. Vincent, 

 Cape de Verde Islands, when the rock pools are 

 exposed by low tides, numbers of sea-urchins (Ecldno- 

 metra) may be seen burrowing in rounded cavities in 

 the rocks, which they had made both in the calcareous 

 sand-rock and the volcanic conglomerate.! In Brazil, 

 also, a species of Echinometra (Ecliinometra Michclint, 

 Dessor) is found living in holes, not only in the sand- 

 stone, but in the gneiss rocks, and in many places the 

 rock is fairly honeycombed by their nests. § 



In Sicily there is a verse which compares the spines 



* Forbes's « British Star-fishes,' p. 170. 



+ Ibid. p. 154. 



X 'A Naturalist ou the Challenger.' 



§ 'Scientific result of Agas.-iz,' "Journey to Brazil," p. 36. 



