BY W. A. IIASWELL. 103 



Genus Pionosyllis MaluigTcn . 

 PioxosYLM.s iielakmixki'jii;a, n.sp. (Plate xii., figs. ]l-l(j; Plate xiii., fls,'. 1.) 



Complete, sexually mature specimens reach a length nL' about 1.4 cm. with a 

 breadth of about 1 mm., and contain 05 to 75 segments. But many specimens 

 show evidence of having lost a part of the fragile posterior region, which has 

 become imperfectly regenerated . Thus a number of specimens contain only about 

 25 to 50 segments of nornud character, with or without a narrow posterior con- 

 tinuation of 3 to 12 sundl segments, obviously formed by a process of regenera- 

 tion . 



The general groun<l-colour in the living animal is yellowish, or greenish, or 

 light pink. On the jn-ostomium, just behind the eyes, is a transverse black line con- 

 cave forwards; this sends forwards a median longitudinal ban<l .vhich bifurcates in 

 front between the eyes. Usually the dorsal surface of the palin is dark with a narrow 

 obliciue light line. Each of the first few segments has a simple transverse black 

 band across its dorsal surface. On a few segments (usually the fifth to the 

 eighth, sometimes a larger number) there is a second transvei-se black band. 

 Further back again each segment has a single band, broad iu the middle, nar- 

 rowing laterally. These bands become shorter posteriorly and disappear alto- 

 gether towards the middle of the body — the posterior part being either devoid of 

 markings or with lighter grey transverse lines. Some black pigment also occurs 

 on the ventral surface of a few of the most anterior segments of the body- 

 Similar pigment is also present in the pharynx, in the proventriculus and in the 

 walls of the nephridia. 



Vibratile cilia are present on the palpi, on the lateral liorders (.if the seg- 

 ments and in groups on the parapodia. Non-motile (sensoi-y) cilia are abundant 

 on the tentacles and cirri. 



The prostomium (Plate xiii., fig. 1) is broader than long. The peri.stomium 

 is visible dorsally for a short distance only. The eyes Aary greatly in develop- 

 ment, but are usually large and may touch or overlap : small frontal eyes are pre- 

 sent. The palpi are large, entirely separate, divergent from close to the base, 

 with an almost oblong outline: but frequently their shape is disguised by various 

 degrees of flexion. In the active living animal they are usually extended almost 

 vertically downwards and folded inwards at the ends, so as fre(|uently to touch 

 one another ventrally in front of the mouth. The prostomial and peristomial ten- 

 tacles are segmented, Imt the segmentation is less distinct towards the base. The 

 median prostomial tentacle is longer than the lateral, longer than the prostomium 

 and palpi together. The dorsal peristomial tentacle, longer thai^ the ventral, 

 is about equal in length to the median prostomial. 



The long, narrow, pointed para]iodia are about e(|ual in length to half the 

 breadth of the segments. At about the 23rd segment, a distinct notopodial rudi- 

 ment with a small aeiculum makes its appearance, and persists throughout the 

 rest of the segments. Each neuropodium has one, two, or sometimes three, 

 aeicula and about fifteen to twenty long and slender compound setae. The 

 acicula (Plate xii., fig. 16) have a conical extremity surrounded at the base by 

 a ring-like thickening. In the compound setae of the anterior region (Plate xii.. 

 fig. 11), the falces, very long and narrow in the case of the most dorsal, decrease 

 in length ventrally, becoming quite short, but ai'e all of the same essential charac- 

 ter: bidontate with the two terminal teeth nearly equal, the cutting edge convex, 

 finely ciliated. Posteriorly (Plate xii., figs. 12-15) a change takes place: the 



