DISTRIBUTION OF THE TERRICOLOUS 



OLIGOCHAETES ON THE TWO SHORES OF 



THE ATLANTIC 



P. Omodeo 



Institute of Biology and Genera! Zoology, University of Siena, Italy 



In order to describe the distribution of the terricolous OHgochaetes that 

 populate the two coasts of the Atlantic. I think the best system is to list the 

 forms that populate the various faunistic districts of America and to describe, 

 case by case, their relationships with those found on the other side of the 

 Atlantic. 



To carry out this review I shall follow Wallace's zoogeographic classifica- 

 tion, which lends itself splendidly to our purpose. 



I shall begin with the Nearctic region (map. Fig. 1). which can be most 

 clearly and briefly dealt with because of its extraordinary poverty. In this 

 region there are 27 species of the Holarctic family Lumbricidae; one species 

 for each of the genera Criodrilus and Sparganophi/iis. of uncertain systematic 

 position but undoubtedly related to the Lumbricidae; about 20 species 

 of Diplocardia (fam. Acanthodrilidae. subfam. Acanthodrilinae); four 

 species of Ilyogenia (fam. Acanthodrilidae. subfam. Ocnerodrilinae); 

 five species of Plutellus (Megascolecidae). Only the genus Diplocardia is 

 endemic in the Nearctic region. 



These animals are not uniformly distributed: in the Canadian subregion 

 we find only a few earthworms belonging to European species, whereas in the 

 more southern Alleghany subregion. which is richest in forms, we find, in 

 addition to the European species, which are always predominant, many 

 endemic species: eight of the family Lumbricidae, twenty of the genus Dip- 

 locardia, and one of the genus Sparganophilus. 



Very few of these forms (Sparganophilus eiseni and four species of Dip- 

 locardia reach the nearby subregion of the Rocky Mountains, where they 

 occupy several stations on the mainland of Mexico and in Lower California; 

 in Lower California we also find four endemic species of the genus Ilyogenia, 

 particular to the Neotropical region and equatorial Africa. Apart from these 

 infiltrations, which concern only the southern districts, the better part of the 

 fauna of the subregion of the Rocky Mountains is made up of European 

 species. 



The Oligochaete fauna of the Californian subregion is also made up of 



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