20 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 39. 



A post-larval specimen with nineteen segments and therefore 

 referable to the variety affinis, was recorded by Ehlers from Uschuaia 

 among the "roots" of Fuciis. 



Summary of the distribution of Arenicola assimilis on American 

 shores. — Typical examples of A. assimilis have been found at Punta 

 Arenas (Strait of Magellan), Uschuaia (Beagle Channel), and South 

 Georgia. 



Examples referable to the variety ajffinis are known from Uschuaia 

 (a gill-less post-larval specimen), Lapataia Nueva (Beagle Channel), 

 Susanna Cove (Strait of Magellan), and the Falkland Islands. 



Further distribution. — Typical examples of A. assimilis have not 

 yet been recorded from any other stations than those mentioned 

 above. The variety afinis is, however, found also at Otago Harbor, 

 New Zealand, and Stewart Island,*^ and at Kerguelen.^ 



Remarlcs on Arenicola assimilis. — The three caudate species of 

 Arenicola — marina, claparedii, and cristata, present a remarkable con- 

 stancy in the number of their ch^etigerous segments and in the seg- 

 ments on which gills are borne. Only in rare cases is an additional 

 chastigerous segment found at the posterior end of the branchial 

 region, and very rarely does this segment bear gills. Among the 

 thousands of specimens of A. marina which have passed through my 

 hands during the last few years I have seen only three with a com- 

 plete chsetigerous and branchiate twentieth segment. 



Ehlers separated A. assimilis from A. marina because in the former 

 the first gill was not on the seventh but on the eighth or ninth seg- 

 ment. But the number of chgetigerous segments is a still more strik- 

 ing character, and, in view of the constancy in the number of these 

 segments in the other caudate species, it seemed to me that the 

 occurrence of examples of A. assimilis with twenty and others with 

 nineteen chsetigerous segments called for recognition. It was on 

 these grounds that, in 1903, I established the variety affinis for those 

 examples of A. assimilis with only nineteen chastigerous segments. 

 The varietal and typical specimens are, however, very closely related; 

 the only differences between them are in regard to the number of 

 segments and the position of the first gill. 



A. assimilis (in the wider sense, that is, including the variety) is 

 clearly the characteristic species of the southern regions. It extends 

 from Tierra del Fuego, by way of the Falkland Islands, South 

 Georgia, and Kerguelen, to New Zealand. The most northerly station 

 from which it has been recorded is Otago Harbor, about 46 degrees 

 south. 



a Unpublished record, from the manuscript of the present writer. 



6 This specimen from Kerguelen, recorded by Grube (Monatsb. K. Preuss. Akad. 

 "Wiss. Berlin, aus dem Jahre 1877, 1878, p. 511) as A. piscatorum Cuvier var., is now 

 in the Koniglische Zoologisches Museum, Berlin. I have recently examined it, and 

 conclude that it is to be referred to the species A. assimilis var. affinis. 



