300 CEYLON PEARL OYSTER REPORT. 



together and calling for no remark) 13 millhns., width 2 millims., total length of body 

 20 millims. 



Polymnia triplicata, n. sp. Plate VI., figs. 149 to 152. 



Locality : Galle, 4th August, 1902. Several specimens. 



This is another tribranchiate Terebellid of small size, with fragile body and highly 

 deciduous tentacular cirri. Length of a specimen, incomplete behind, 35 millims. ; 

 thorax barely wider than rest of body, 3 millims. in diameter, with 17 setigerous 

 segments ; abdominal portion with 34 pinnigers. Another abdominal fragment had 

 80 segments. 



The second, third, and fourth segments (the fourth being the first setigerous 

 segment) carry lateral lobes of approximately ecpjal size (Plate VI., fig. 149). The 

 scuta ventralia are 14 in number, counting from the second segment; they end 

 sharply on the 13th setigerous segment, leaving four setigerous (thoracic) segments 

 without ventral shields. The central portions of the scuta are slightly marked off 

 from the anterior and posterior borders, but otherwise they are simple, not biannulate 

 nor areolated. 



The arrangement of the anterior thoracic segments seems to differ considerably 

 from the condition observed in P. labiata. As shown on Plate VI., fig. 143, there is, 

 in P. labiata, a large lower lip with free sinuous border, considered as belonging to 

 the second segment (i.e., the first branchiferous segment) and followed by another 

 acheetous segment (the second branchiferous segment) carrying prominent lateral 

 lobes. In P. triplicata the lower lip is followed by two achsetous segments carrying 

 lateral lobes, and also bearing the first and second pairs of gills. It appears, therefore, 

 that in P. labiata and in the species of Loimia the much larger lower lip is a product 

 of the fused first and second segments, while in P. triplicata the first and second 

 segments are distinct below, the former alone carrying the lower lip. In this and in 

 other respects (number of scuta, &c), the present form offers a striking analogy to 

 Lanice triloba described by Fischli from Ternate,* and were it not for the existence 

 of the generic distinction, which is not apparent at the surface, the two species would 

 probably be ranged together. 



The enumeration of the anterior segments and the nature of the prostomium of 

 Terebellidae are matters of some obscurity. On Plate VI., fig. 149, the thin half- 

 collar which overhangs and protects the mouth like an epistome or upper lip is seen 

 in side view ; at the back of it are the scars of insertion of the tentacular cirri, 

 followed by a clear surface of a segment showing numerous eye-spots. Then follow 

 the gills on the second, third, and fourth segments. The uncini are much smaller than 

 in P. labiata, and usually only one denticulation of the third order is to be observed 

 (Plate VI., figs. 151 and 152). The dorsal portion of the thoracic segments becomes 

 biannular, commencing from the region of the eighth torus (Plate VI., fig. 149). 



* H. Fischli, "Polychiiten von Ternate," ' Abh. Senckenberg. Ges.,' xxv., 1900, p. 122. 



