252 CEYLON PEAEL OYSTER REPORT. 



individual examined. The number 18 is a generic character of Acanthicolepis, McInt. 

 (= Dasylepis, Mgn.), but it seems likely, though not certain, that a polymeric 

 Polvnoid with more than 18 pairs of elytra will pass through a stage with 18 only. 

 At any rate, Polynoe venosa, Gr., does not belong to the genus Acanthicolepis. 



Those polymeric Polynoidse in which the paired antennae arise at a lower level than 

 the tentaculum impar appear to be inadequately classified. Malmgren's genera 

 Nemidia and Enipo are at most only sub-genera of Schmarda's Hemilepidia. 



All Polynoidae (s. str.) in which the antennae arise at a lower level than the 

 tentaculum are placed in the sub-family Harmothoina. The genus Polynoe (s. str.) is 

 polymeric, having more than 45 segments in the fully formed condition. It comprises 

 two sections: (1.) Hemilepidia, Schmarda, in which there are 15 pairs of elytra 

 restricted to the anterior region of the body. This section comprises the following 

 species : Polynoe scolopendrina, Hemilepidia erythrotcBnia, Nemidia torelli, and 

 Enipo kinbergi. (2.) Hololepidella, n.g., in which the elytra are not so restricted. 

 Very possibly Grube's Polynoe venosa belongs here in spite of its few segments. The 

 species now described also belongs to this section. 



In Hololepidella commensalis the small antennae clearly arise at a lower level than 

 the tentaculum (Plate I., fig. 20). The elytra are pale, delicate, translucent, smooth, 

 large, orbicular, covering the back ; the first pair with central insertion, the others 

 with excentric insertion near the anterior margin becoming submarginal in the 

 posterior region ; there is an indication of nervures radiating out from the scar of 

 insertion, as in P. venosa. The elytra are inserted upon segments II., IV., V., VII., IX. 

 * * * * * XXL, XXIII. , XXVI, XXIX., XXXI. , XXXIV, XXXVI, XXXVIII., 

 XL., XLIL, XLV. ; segment XLIV. has an elytrophore on the left side, a branchial 

 tubercle and cirrophore on the right side. There are 46 segments present, incomplete 

 behind ; in a fragment of the posterior end the alternation of cirrophores and 

 elytrophores, the former sometimes skipping one segment, sometimes two, seems to be 

 continued to the end of the body, but it is not always easy in this region to distinguish 

 between a cirrophore and an elytrophore. 



Head hexagonal ; ground colour of body nearly black (becoming brown after a 

 length of time in spirit) with a pale ridge across each segment between elytrophores 

 and branchial tubercles respectively. Palps, antennae, tentacle and cirri smooth ; first 

 ventral cirrus long, the rest short, with swollen basal portion and terminal flagellum. 

 Dorsal cirri dark brown, tapering to a pale blunt point which may be slightly swollen, 

 but without subterminal dilatation. The setae are pale ; dorsal setae, about 8, broad 

 parce-serrulate, much shorter than the ventral setae ; superior ventral setae obliquely 

 laciniate towards apex, giving the appearance of alternate serrulations, inferior ventral 

 setae with subterminal dilatation, curved simple tip and normal fringes (Plate I., 

 figs. 17 to 19). 



This species is one of those which easily undergo fragmentation, so that the length 

 cannot be given ; the width is 2 millims. 



