ZOOGEOGRAPHY 369 



on the pselaphid fauna of the United States, shows that the then known fauna 

 compared very favorably with the even far better known pselaphid fauna of 

 Europe. Also, this is not to say that a great deal has been done in Nearctic 

 pselaphids — there are many new species undiscovered, no thorough zoogeog- 

 raphy — the large size of the Brazilian fauna simply means that the neotropics 

 abound in these beetles. 



The lowest taxonomic density (area divided by species) is in Ecuador, 

 1 species per 116,000 square miles. The highest t.d. is in the Isthmus of Panama, 

 1 species per 410 square miles, as far as the mainland is concerned. As seen in 

 the following table, certain Antillean groups have a higher taxonomic density. 



Table IX 



TAXONOMIC DENSITY OF NEOTROPICAL PSELAPHIDAE 



Country 



Taxonomic Density- 



Virgin Islands . . . 

 Windward Islands 

 Leeward Islands . . 



Panama 



Puerto Rico 



Guatemala 



British Honduras . 



Costa Rica 



Paraguay 



French Guiana . . . 



Chile 



Mexico 



Cuba 



Venezuela 



Colombia 



Brazil 



Hispaniola 



Bolivia 



Nicaragua 



Dutch Guiana . . . 



Argentina 



Honduras 



Peru , 



Uruguay 



British Guiana . . . 

 Ecuador 



26 

 53 



410 



850 



964 



2,150 



2,875 



4,652 



5,333 



6,440 



6.909 



7,333 



7,381 



7,471 



9,221 



9,400 



11,422 



12,300 



15,333 



23,530 



44,200 



70,980 



72,000 



89,500 



116,000 



These ratios merely reflect our present state of information, and show no 

 relation to size of range, but when we consider that much of the Neotropical 

 Region is occupied by a single biome, namely the Rain Forest, with abundant 

 moisture, food and vegetation, it is clear that the taxonomic densities, at least 

 between the Tropics of Cancer and Capricorn, should approach each other at 

 last. That is, a unifonn biome should have a uniform taxonomic density, other 

 conditions remaining favorable. 



But what is this maximum taxonomic density? To reach an approximate 

 answer we must return to the best known area. This is a rocky, little mountain 

 peak, Barro Colorado Island, cut off when the Chagres River was dammed in 

 1914 to form the Panama Canal. It lies in Gatun Lake, athwart the north-south 



