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[Communicated Maj- 22(1, 1S60.] 



Mr. Lea called tbe attention of the members to two very remarkable speci- 

 mens of Echinus, perforating rocks, which he had recently received from Mr. 

 Cailliaud, of Nantes, tbe Egyptian traveller. He also exhibited a specimen of 

 Sandstone from Payta in Peru, which contained Petricola, Lithophagus, &c. He 

 reminded the members that he had presented to the Academy a very remarka- 

 ble specimen, which he had received about two years since from Mr. Cailliaud. 

 iieing a mass of gneiss which had been perforated by Pholades. When Mr. 

 Cailliaud, who had advocated, contrary to the opinion of most naturalists, the 

 theory that some of the Molluscs bored the rocks by friction and not by de- 

 composition, found that gneiss and granite and other silicious rocks were pene- 

 trated by them, he entirely settled that question, for there are no acids known 

 which will decompose silex. Mr. Lea remarked that the two specimens now 

 on the table were still more remarkable. The smaller one consisted of two 

 specimens of E-hinus lividus, Lam., which had buried themselves in the solid 

 granite, one of them having made a circular hole U inch deep, and 2 inches 

 wide. This specimen came from the granite coast of the Loire-Inferieure 

 The second specimen consisted of quite a congress of individuals of the same 

 species, imbedded in a solid mass of hard Silurian Sandstone, from the Bay of 

 Douarneuez, in the Department of Finistere. In this beautiful specimen there 

 are five individuals nestled in their circular holes, worked out in this hard stone 

 by the attrition of their teeth, and there are three holes vacated. The specimen 

 is 5 inches by GJ, and there being eight holes in all, their circumferences nearly 

 impinge on each other. Mr. Cailliaud is entirely satisfied that the boring is 

 purely mechanical, that the fire teeth are the instruments of exploitation, and 

 that it is by the percussion of their points on the rocks that these holes are 

 •■ffected. The teeth are in form like the rodents, and constantly increase as 

 worn at the outer extremity. He made a hole five millimetres deep and forty 

 in circumference with a bundle of the teeth in an hour. One of the colonies 

 which he examined was in a bay, and contained about two thousand holes, each 

 one filled, and at low water they were but a short distance below the surface. 

 Some of the specimens were not larger than a pea, and probably only five days 

 >ld. The holes were not all made by the present occupants, most of them pro- 

 bably being very old and having successive inhabitants. Mr. Cailliaud men- 

 tioned in his letter to Mr. Lea that he shortly expected to receive from Guada- 

 Icipe an oval Echinus which had made its oval hole in the mass of Madreporitt. 



