POLYCILETA OF PLYMOUTH. 601 



synonymy of the three forms of Syllis which have been described 

 by different authors under the names, Syllis prolifera Krohn, 

 S. variegata Grube and S. hyalina Grube. After examining a con- 

 siderable number of living specimens my own view is that two 

 distinct species have been referred to under these names, which 

 would most conveniently and probably according to the law of 

 priority most correctly bear the names S. frolijera Krohn and 

 S. variegata Grube. The name S. hyalina Grube has I think most 

 frequently been apphed to examples of S. prolifera (and possibly 

 other species) which were not yet fully grown.* In S. prolifera 

 Krohn the pharynx is comparatively short and stout, the single dor- 

 sal tooth is large and is usually situated at the hinder end of the 

 first third of the pharynx. There is a considerable distance between 

 the point of the tooth and the anterior edge of the pharynx. 



The proventriculus is comparatively short and stout, being 

 about the same length as the pharynx. 



The end pieces of the bristles have very boldly bifid tips, the 

 bifid character becoming moTe and more marked in the posterior 

 segments, where the end pieces also become much shorter. 



In the last few parapodia there is in each a single straight simple 

 bristle dorsally, the tip of which is often with some difficulty seen 

 to be bifid, and ventrally a single curved simple bristle with a boldly 

 bifid tip exactly resembhng the tip of the compound bristles. 



The anterior segments contain a quantity of brown pigment on 

 the dorsal surface. This pigment is in many specimens distributed 

 fairly uniformly over the surface, but more generally it tends to 

 accumulate along the posterior border of the segment forming a 

 transverse brown bar. In other specimens again in addition to this 

 posterior bar there is an accumulation of the pigment in the centre 

 of the dorsal surface of the segment, a brown patch above each of 

 the dorsal cirri, and a bar along the anterior border of the segment. 

 The pattern thus formed tends to resemble that of S. variegata, 

 but this pattern is not often found in S. prolifera, in which the 

 uniform distribution of pigment on the dorsal surface with a pos- 

 terior bro\^Ti bar is the more characteristic condition. 



The dorsal cirri are moniliform. They are distinctly long, as 

 compared for example with S. armillaris or S. gracilis, and in well- 

 grown worms have from 25 to 30 or even 40 articulations. They 

 differ in length, being alternately long and short throughout the 

 greater part of the body. 



The Pionosyllis hyalina Grube described by Mcintosh (Mon. 

 Brit. Ann. II. 1, 1908, p. 166) is almost certainly this form in an 

 immature condition, with the cirri not yet fully grown and thus 

 having fewer articulations. 



* It should be noted that the S. hyalina of Malaquin is the 8. alternosetosa de St. Joseph, 

 recorded in the present list as S. armillaris (Miiller) (Rech. sur les Syllidiens, 1893, p. 96). 



XEW SEUIES. — VOL. X. XO. 4. MAY, 1915. 2 Q 



