OLIGOCHAETA 



PART I. MICRODRILI (mainly ENCHYTRAEIDAE) 

 By J. Stephenson, M.B., D.Sc, F.R.S. 



(Text-figs. 1-14) 



INTRODUCTION 



THE Microdrili in the present collection have been obtained from four localities: the 

 Palmer Archipelago, almost directly south of Cape Horn, near Graham Land, 

 between 64° and 65° S lat.; the South Orkneys, between Graham Land and South 

 Georgia, in S lat. 60-61°; South Georgia, approximately in S lat. 54-55° and W long. 

 38° ; and Gough Island, in the middle of the South Atlantic, somewhat to the south-east 

 of Tristan d'Acunha, in S lat. 40°. These places are more or less in line with each other, 

 the line stretching from south-west to north-east, from the Palmer Archipelago to 

 Gough Island ; but Gough Island is at a considerably greater distance from the other 

 localities than these are from each other. 



Apparently no Microdrili have previously been collected in the Palmer Archipelago, 

 the South Orkneys, or on Gough Island; but from South Georgia we possess the 

 records of Michaelsen (1888) and Michaelsen (1905) {Hesperodrilus crozetensis, Rhyaco- 

 drilus coccineus, Marionina georgiana, M. exigiia, Lumbricilhis maximus, Ettchytraeus 

 albidus, Michaelsena monochaeta). While Marionina exigua, Rhyacodrilus coccineus, and 

 (apparently) Hesperodrilus crozetensis have not been recovered by the present expedition, 

 the tubes from South Georgia contain the other species previously found there, and in 

 addition Marionina aestuimi, sp.n., Liimbricillus antarcticus, sp.n., L. macquariensis 

 (known previously from the sub-Antarctic islands of New Zealand), Enchytraeus 

 aiistralis, sp.n., E. colpites, sp.n., a probably undescribed species of Hesperodrilus, and 

 an indeterminable specimen belonging to the genus Achaeta. 



My best thanks are due to the authorities of the British Museum (Natural History), 

 where my investigations were carried out, for the facilities so kindly afforded me. All 

 the specimens, including types of the new species, are now in the Museum. 



GEOGRAPHICAL DISTRIBUTION 



The facts of distribution of the earthworms (Megadrili) of the sub-Antarctic islands 

 are of interest as contributing to a discussion of the problem of an Antarctic Continent 

 and its former connections as a factor in zoogeography. The problem has been argued, 

 principally by Michaelsen and Benham, on the basis of the present-day distribution of 

 the acanthodriline genus Microscolex; and I have recently (Stephenson, 1930) given an 

 outline of their arguments, with references to their papers. Briefly, Benham sees the 



