47 30 Proceedings of the Royal Irish Academy. 



Opisthodonta Langerhans. 



This genus was created by Langerhans (1879, p. 547) to include a species 

 found at Madeira, with separate palps, smooth unjointed cirri, and a single 

 tooth in the posterior part of the pharynx. It differed from the genus 

 Pionosyllis in the position of the tooth in the pharynx. Malaquin (1893, 

 p. 69) maintained the genus, and stated in a foot-note that he had examined 

 a species belonging to this genus from the Mediterranean, at Banyuls-sur- 

 Mer, which differed from that of Langerhans. So far as I know, it has not 

 yet been described. The species from Clew Bay differs considerably in the 

 structure of the spines and setae from 0. morena Langerhans, and for the 

 present no generic characters can be based on these characters till the 

 Madeira species has been more fully described. It was an immature speci- 

 men ; but the Clew Bay specimen confirms the opinion one would derive from 

 the systematic relations of the genus, that reproduction is direct, the worms 

 at maturity developing swimming setae and becoming pelagic. 



Opisthodonta pterochaeta sp. n. 



PI. IV, figs. 6A-G. 1 



The anterior end only of a single specimen was available for this descrip- 

 tion. It belongs to a mature male, with swimming setae developed, and was 

 taken in October in the mid-water tow-net at 9 fathoms, in soundings of 

 18 fathoms, one mile north of Cleggan Head. 



This fragment is 6 mm. long, and consists of 49 setigerous segments. 

 At its widest part, it is - 7 mm. wide; and it tapers considerably towards the 

 anterior end. The head (PI. IV, fig. 6b) is rounded in front, with a straight 

 posterior margin. It bears four large reddish-brown eyes, with lenses. The 

 median tentacle, which is missing, rises between the anterior eyes. The lateral 

 tentacles rise near the front of the head. All these appendages and the 

 other cirri of the body are smooth and cylindrical, with no trace of articula- 

 tions. The palps are of medium size, free distally, but united at the base, 

 with rounded angles. The buccal segment is distinct dorsally, though slightly 

 narrower than the subsequent segments, and bears two pairs of tentacular 

 cirri. Of these the ventral pair are rather longer than the lateral tentacles, 

 whilst the dorsal pair are twice as long. 



The pharynx (PI. IV, fig. 6a) is very long, 14 mm. in length, dark-brown 

 in colour, and stretching through 16 segments. Just behind its middle point 



1 The figures for this species and for Microphllialmw Sczelzot'.-i, which by error have both been 

 numbered 6, may be distinguished by the number of the plate. 



