124 THE NAUTILUS. 



sixty-tliree years ago. Forces capable of clianging habitat and habit 

 might cliange form and characteristics. ' 



My metliod in collecting is to traverse the beaches and from dead 

 or bn.kt'n fragments of shells, observation of tide currents, eddies, 

 and prevailing winds, mark out probable stations at low water or 

 beyond. Tlie metiiod is seldom wrong and leads to live specimens, 

 either for wading or dredging, in shortest time. 



Some s])ecies in Panama Bay have gone to other stations. Some 

 have disappeared. Kearly all have sought deeper water and stay 

 there. 



Very solid volcanic rock, some of it nearly pure iron, is continu- 

 ous from two miles west of Panama City to Taloga Island, fourteen 

 miles. 'J'he Canal runs through part of it, and over the lest of this 

 strata. Heavy dynamile blasts on the main land and on the islands I 

 in the Bay where Canal foilifications are to make another Gibraltar, 

 can be felt di.-tinctly at Taboga, too far away to be lieard, sometimes. 

 These concussions are frequent, occuiring many times a day. A 

 breakwater extends from the mouth of the Canal to the island forti- 

 fications. This breakwater is tuo miles long, and all day long train- 

 loads of dynamited lock are dumped into the waters of the Bay on 

 either side. It is possible that four years of concussion and waters 

 more or less poisoned by nitroglycerene, plus the sewerage of Pan- i 

 ama, may have destroyed food and driven the species to new stations, 

 to deeper water, or worse, destroyed many of them. The volcanic 

 reef ends abruptly a mile out and the water suddenly deepens to ! 

 thousands of feet. At Taboga the conditions are more favorable i 

 and there is superb collecting ground, but even there low tide does , 

 not expose the live species — to any encouraging extent. The infer- 

 ence that all Panama species near the Canal have sought deeper j 

 water is justified. I 



Theie is a big suction dredge at Balboa near the mouth of the 

 Canal. This dredge takes up everything from bed rock to top sand 

 and sends a twelve-inch stream of water, mud, and millions of shells , 

 (seldom alive), a mile or two inland to make new land. Most of 

 these shells have not been dead long, some are semi-fossil. There i 

 is fine collecting at the end of that pipe. But specimens taken there | 

 indicate wholesale destruction of molluscan life at the mouth of the 

 Canal. 



The most interesting " station " however on the Isthmus is in 



