Clare Island Survey — Archiannelida and Pob/chaeta. 47 1 1 1 



the same species. Not one of them has been adequately described or 

 figured. 



Habitat. — Clew Bay — Dredged in Inishlyre Harbour in 5 fms., on mud. 

 Killary Harbour — Dredged on two occasions in 7 fms., on 

 mud. Bofin Harbour — Taken at night in the tow-net. 

 Distribution. —West coast of Norway. 



Genus Chaetozone. 



The genus Heterocirrus was created in 1S55 by Grube, for a species he 

 named H. saxicola. This species was afterwards shown to be the Bodecaceria 

 concharum of Oersted, described in 1843. De Saint-Joseph (1894, p. 52) 

 conserved the genus Heterocirrus, whilst giving it a new definition ; but this 

 is contrary to the Bules of Nomenclature ; and Moore 1 adopted what, in his 

 opinion, was the next available name, the Tharyx of Webster and Benedict 

 (1887, p. 741). 



The genus Chaetozone was created by Malmgren in 1867 ; but he gave no 

 generic diagnosis. In the opinion of subsequent writers, the distinguishing- 

 character of this genus was the modification of the setae in the posterior part 

 of the body, where they form an almost complete ring, consisting of a mixture 

 of crochets and capillary setae. Caullery and Mesnil (1898), in reviewing the 

 genera of the Cirratulidae, retain the three genera Heterocirrus, Tharyx, and 

 Chaetozone, defining them by the structure and arrangement of the setae. In 

 Heterocirrus, crochets are present in the dorsal and ventral rami ; in 

 Tharyx all the setae are capillary ; and in Chaetozone the crochets form an 

 almost complete ring in the posterior segments. In practice this classifica- 

 tion breaks down hopelessly. For instance, the Chaetozone zetlandica of 

 Mcintosh (p. 115) has crochets in the ventral rami, and capillary setae in the 

 dorsal rami. Again, the degree to which the crochets form a ring on the 

 posterior segments is very variable ; and it is impossible to draw a distinction 

 between Heterocirrus and Chaetozone in this respect. There is reason to 

 think that some species which have crochets when fully grown have only 

 capillary setae in their earlier stages. The marked development of the crochets 

 in Chaetozone is evidently an adaptation for a pelagic life — an adaptation 

 which exists in various degrees in all species of the three genera, and is a 

 character to which no generic importance can be attached. 



In view of these facts the conclusion is irresistible that no valid distinction 

 exists between the three genera. Chaetozone has clearly priority over 

 Tharyx, and hence must be used, with Chaetozone setosa Malmgren, as the type 

 species. 



1 Proc. Acad. Nat. Sciences of Philadelphia, 1909, p. 268. 



