1897.] NEW YORK ACADEMY OF SCIENCES, 215 



berg, Fellow in Botanj'-, for assistance in translating the Swedish 

 article of Wiren. 



I. Introduction, 



II. Nature of the Commensalism. 



III. Heteronereis and Nereis forms. 



IV. Relation of Old and New World types. 



V. Detailed Description of Nereis cycluriis, n. sp, 

 YI. N. fucata Sav., the European species. 



I. Introduction. 



From depths of from ten to twenty fathoms in Fuget Sound 

 baj-s the dredge brings up Lunatiaa, Notica, Argohuccinum, 

 Fusus and Plerenotus from bottoms covered with laminaria and 

 various algae. The empty shells of these mollusks are inhabited 

 by Eupaguriis splendescens, E. tenuimanus^ E. armatus and E. 

 turgidus. Those of largest size are E. armatus, Dana, which 

 sometimes reach eight inches in length. As these crabs slowly ad- 

 vance from their retreats, one or two or sometimes three beauti- 

 fully striped Nereids will emerge from the opening of the shell, 

 and, if the crab be feeding, will proceed to the mouth parts of the 

 latter and share the feast. Exposed in this way for about 

 twenty or thirty somites, their resemblance to the thoracic legs 

 of the crab in color, size and action is very striking. If dis- 

 turbed they withdraw with a sudden ierk to the innermost coils 

 of the shell, where in old and crumbling shells of Lunatia the}' 

 have a communication with the hollow umbilicus. The}^ do not 

 bore tunnels into the columnella as does Poly dor a commensalis. 

 The large Nereids are usually restricted to Lunatia and Natica 

 shells with E. armatus, but we have found them in Pterenotus 

 shells, and a ver}' small Nereid with E. termimanus. We have 

 not as yet found any allied free-living Annelid, although the 

 European species, N. fucata, has (1) an atocous form which 

 lives on the bottom gravel in shallow water, under stones, shells 

 and laminaria — and (2) an epitoeous form, $ , which is pelagic. 



II. Nature of the Commensalism. 



Nereis relies upon the hermit-crab for food, protection and 

 locomotion as do the other members of the philozoic institution 

 supported b}^ Pagurids. The highly developed sense organs and 

 weapons of offense of the annelid indicate that the Nereid 

 furnishes something towards the household economy. The fol- 

 lowing interesting experiment is recorded of the Swedish forms. 



