Mollusca of St. Andreici. 345 



gepliyreans, and cirrlpedes, nor by a comparison of the 

 siiells and tunnels of the mollusks themselves. The 

 epidermis of the latter in each case would likewise suffer. 



II. That the holes are made by rasping effected by siliceous 



particles on the foot of the mollusk (Hancock), by grains 

 of silex from the exterior (Bryson), by the foot in some 

 way (Dr. Fischer), and by chitine in the cirripedes 

 (Darwin) and gepliyreans and the bristles of the annelids. 

 This explanation is not borne out by the case of the 

 sponges, by that of the Bryozoa, and certain cirripedes ; 

 moreover such siliceous particles are rare in boring 

 mollusks. 



III. That the excavations arc due to ciliary currents, aided 

 by rasping (Garner). 



The currents may assist, but seem to be insufficient to 

 account for the borings in any group. 



IV. That the perforations are produced by a chemical solvent : 

 Gray, Osier {^ox Saxicava) , Drummond,Cailliaud, Mantell, 

 Thorent, Reeve, Bouchard- Chan tereaux, Spence Bate, 

 Darwin (for Verruca), E. R. Lankester, and Parfitt. 



This will not explain the borings in wood, aluminous 

 shale, gneiss, granite, sandstone, and wax. It is interest- 

 ing, however, as my friend Mr. Ray Lankester has spe- 

 cially shown, that shells and calcareous rocks are much 

 affected by burrowing marine animals. 



V. That the borings are the result of a secreted solvent and 



rasping action (Thompson and Necker). 



It seems improbable that the solvent should vary with 

 the nature of the rocks attacked. 



VI. That the perforations are caused by a macerating or simple 

 solvent action of the foot in mollusks (Sellius, Deshayes, 

 and Gwyn Jeffreys). 



It is doubtful if this would be supported by the action 

 in the sponges, Bryozoa, annelids, gephyreans, and ciiTi- 

 pedes. The strise in certain of the tunnels of the shell- 

 fish are also somewhat at variance with this notion. 



The most interesting species in regard to rarity are Lima 

 suhauriculata and L. Loscomhii^ which come from deep water, 

 the characteristic Lima hians of our southern and western 

 shores being.absent. A worn valve of Isocardia cor found on 

 the West Bands is purely accidental. Tellina pusilla and 

 Psammohia tellinella are uncommon at St. Andrews. Amongst 

 univalves, Trichotropis horealisj Pleurotoma Trevelyana, 



