284 \Trmisactions of the Society. 



Mich.), and from those of the next group by the absence of capilli- 

 form setse or bristles. Beddard's definition of the genus is as 

 follows : — " Setse uncinate, except dorsal setse of v-xiii, which ore 

 mainly palmate. Dilated hearts in viii. Spermiducal gland 

 divisible into two regions ; the glandular region (vesicular) not 

 dilated ; penis chitinous ; prostates present." 



1. Heterochieta costata Clap. 



Benham has elaborated the definition (Q.J.M.S., xxxiii. (1891) 

 p. 187 et seq.). Writers draw attention to the variation in the 

 number and arrangement of setse ; but as these variations are in 

 some instances accompanied by differences elsewhere, the species 

 will eventually be found to number more than two, as at present 

 diagnosed. My own material, collected in Ireland, Cumberland, 

 Lancashire, the Thames, and elsewhere, needs careful working out 

 before pronouncing further on the subject, and I therefore pass on 

 to the other species, merely noting the occurrence inland as well as 

 on the shore. 



2. Heterocha'ta Tliom'psoni Southern. 



Bright red. Length about 20 mm. Anterior dorsal setse 

 closely resembling those oi H. costata, and found in segments 5 to 18, 

 7-10 per bundle. Eemaining dorsal bundles with forked setse only, 

 teeth equal. Brain concave before and behind. Nephridia large, 

 no peritoneal cells. Spermathecse sac-shaped, long, extending into 

 segment 9. Nail-shaped penial seta in sac ; and apparatus dis- 

 tinctly different from that of latter species. 



Eock pools, Howth, co. Dublin. 



GROUP II. — Capillifokm Set.e Present. 



A. — Forked Setse with Capilliform in Dorsal Bundles. 

 Pectinate Setae wanting. 



I cannot too strongly emphasize the fact that the confusion 

 which has up till the present existed in this family is almost en- 

 tirely due to non-observance of the point that some genera have, 

 and some have not, pectinate seta3. I deal first, therefore, with those 

 genera which have forked setse only with the capillary or hair 

 bristles. It is now possible, for the first time, to bring Ilyodrilus 

 definitely into the British lists. But Ilyodrilus is at present in 

 confusion, since it has been differently defined by Eisen, Stole, 

 Ditlevsen, and others. Beddard attempted to place things right, as 

 also did Michaelsen ; but Ditlevsen's researches introduced further 

 confusion, since he places Rhyacodrilus with Ilyodrilus, and what 

 is undoubtedly a true Ilyodrilus imder Monoirylepkorus. Though 



