2 BULLETIN 122, UNITED STATES NATIONAL MUSEUM. 



The history of systematic zoology and botany, too, for that matter, 

 is replete with examples showing that the men of science have ever 

 tried to keep down the number of specific names by stretching the 

 definition of some previously described form to embrace the organ- 

 ism they had in hand. This superconservatism has caused more mis- 

 chief in the proper understanding of many groups of organisms than 

 any other single factor. 



The layman who wishes to attempt an understanding of this mass 

 of misconcepts will find himself in an interminable maze of synonyms 

 and homonyms in which most signposts will be Greek to him, and, 

 confused and confounded, he will turn the matter over to the 

 specialist. 



Now, unfortunately, the specialists, even to-day, have not the ade- 

 quate material to definitely decide many points, but each succeeding 

 year has seen an accumulation in our larger museums, even fragmen- 

 tary as it usually is, of material gathered in many places, and by this 

 means we are able to slowly forge our way from the hazy mists of the 

 past into the clearer viewpoint of to-day. 



Accumulated material, then, makes it possible for us to say that 

 the shipw^orms are no law unto themselves,^ but are subject to the 

 same limiting influences that govern the geographic distribution of 

 other bivalve mollusks, and it is safe to state that the shipworms 

 are as particular about their habitat as the other members of the 

 phylum. 



In spite of the fact that the shipping of the past in wooden bot- 

 toms offered an exceptional opportunity for the universal distribu- 

 tion of these pests, little of the kind seems to have been accom- 

 plished. Most of the exotic material thus obtained consists of dead 

 pallets and shells entombed in the wood which they had affected. 

 Such records can scarcely be accepted as genuine residents of the 

 geographic place from which they were obtained. Thus it would 

 be wrong to list as European, species encased in mahogany logs or 

 coconut husks, and carried by the Gulf Stream's drift to Norway, 

 Sweden, or the British Isles, where an unsuitable environment pre- 

 vents them from propagating or establishing their kind. Were 

 shipworm colonization merely a matter of transportation, then we 

 should find the shores touched by the great ocean currents peopled 

 by the same species, and this is not the case. The sea, like the land, 

 has its environmental barriers, and the zoogeographic areas sepa- 

 rated by them contain faunas just as peculiar to them as zoogeo- 

 graphic areas on land contain land animals peculiar to these. On 

 land we have the elements of suitable habitat temperature, moisture, 

 altitude, length of day, food, and other environmental factors. In 

 the sea we have suitable habitat temperature, salinity, depth, light. 



