VI LIST OF PLATES. 



3. Teredo navalis, or Sliip-wonn, in a piece of timber wliicli lias 



been perforated by many other individuals. The white 

 tube is broken, to show the worm-like animal, with the 

 pallets inserted at the upper end, where it is divided into 

 the two canals. At the lower end the valves are shown, 

 and the little sucker-like foot, supposed to be a chief agent 

 in excavating the wood. 



4. One of the separated pallets of T. navalis. 



5. One of the horny, pen-shaped pallets of T. hlpennata. 



6. Valves or shell of T. Norvegica. 



Plate III. 



BORERS AND BURROWERS. 



1. Xylophaga : like a Teredo, but ^\dthout a tube. The boring 



has been effected r/cross the grain of the wood. 

 3. Gastrochana modiolina, valves and animal. 



3. Yalves of the same alone. 



4. Tube or case made of pebbles, sand, etc. agglutinated, con- 



taining the valves and animal inside. 



5. Saxicava arctica. 



6. PJioladidiea jMjjyracea, or Paper Pholas, with a horny cup at 



the end of the valves. 



7. Petricola litliophaga ; literally, "rock-inhabiting stone-eater." 



Plate IV. 



1. Necera cuspidata, showing the shell with the foot and tubes 

 of the animal. 



