Clare Island Survey — Archiannelida and Polychucia. 47 115 



dorsal bundle is much larger than any of the others in either division. The 

 upper crochet in the ventral division (fig. 28d, b) is larger than the lower ones 

 (fig. 28d,c). The tip of the crochets is curved, and the two points diverge 

 at a very wide angle (fig. 2Se). 



So far as can be seen from the available specimens, there is no tendency 

 for the posterior setae to form a ring round the segment, such as characterizes 

 Ghactozonc setosa and other species. However, as all the specimens except 

 one fragment are immature, it is possible that considerable changes take 

 place in the setae at the period of sexual maturity. This species is closely 

 related to GIufMosam zetlandica Mcintosh, but differs in having no eyes, in 

 having crochets in the posterior dorsal bundles, in the relative position, size, 

 and shape of the setae, etc. It differs from CJiactozone caput-esocw (de 

 St. -Joseph) in having no eyes, in having bifid crochets, and in the position, 

 shape, and numbers of the crochets. 



Habitat. — Dredged in Killary Harbour, in 7 fins., in rich black mud. 



Chaetozone zetlandica Mcintosh. 

 Pis. XII, XIII, figs. 29a-k. 



1911. Chaeio-one zetlandica. Mcintosh, p. 161. 



This species was recently described by Mcintosh from a single fragment 

 consisting of the posterior end of a specimen dredged in 100 fathoms in 

 •St. Magnus Bay, Shetland. It is at once distinguished from all other species 

 of the genus by the arrangement of the crochets, which are present in the 

 ventral, absent in the dorsal bundles. Through the courtesy of Professor 

 Mcintosh, I was able to examine the type-specimen, and compare it with the 

 individuals here described. Consequently any errors which may be involved 

 in the assumption here made that the various forms described below are 

 referable to one specific form — C. zetlandica Mcintosh— will be due either to 

 the fragmentary nature of the type-specimen, or to the wrongful interpre- 

 tation of alterations in structure clue to growth and development. 



Altogether, 25 specimens are available for study. These can be easily 

 divided into 3 stages, the most obvious distinction being the size. These 3 

 stages will be considered separately. 



Stage A. — The occurrence of this form is worthy oi note. Twenty-three 

 specimens were Uiken, on ten different occasions in the months of March — 

 August. These specimens were always captured at night, in the tow-net, 

 usually at the surface, and have only been obtained in Fahy Bay, a branch 

 of Ballynakill Harbour. 



These worms are 4-6 mm. long, composed of 36-64 segments, of which, 

 in the larger specimens, 40—50 are provided with cirri. The shape of the 



P2 



