2G6 CEYLON PEARL OYSTER REPORT. 



The head itself, under the condition of extruded pi'oboscis, is about as broad as 

 long and not deeply notched behind. On each side of the prostomium there is a 

 prominent lateral nuchal papilla. The phyllodes resemble those of Ph. macrolepidota 

 in shape and proportion, the dorsal phyllode being distinctly pedunculate and its axis 

 occupied by a rete mirabile, from which radial vessels proceed to the margins. The 

 parapodium carries twelve setae of normal type (Plate III., fig. 73), though, as shown 

 by M. Gravier, the number varies within narrow limits in different regions of the 

 body. The number which I have given holds good for the mid-region. A foot from 

 the posterior region has sixteen setae. 



Pterocirrus ceylonicus, Mtchaelsen. 



This species is well characterised by the five long slender subequal prostomial 

 appendages, longer than the prostomium. The remarkable winged ventral cirrus 

 of the second segment which, seen from above along its thickened dorsal border, 

 looks like an ordinary tentacular cirrus, is a generic feature of first importance. 

 The dorsal phyllodes are more lanceolate than that shown in Dr. Michaelsen's 

 figure, "Polychiiten von Ceylon," ' Jahrb. Hamburg. Wiss. Anstalt,' 1892, ix., 2, p. 103, 

 otherwise I have nothing to add to his description. The colour of the preserved 

 specimens is dark greenish-brown. Locality : Ceylon Seas. 



Family : HESIONID/E. 

 Hesione ceylonica, Grube. 



Grube, "Ann. Ceylon" (Holdsworth coll,) ' P. Zool. Soc. London,' 1874, p, 327. 



Locality : Numerous specimens from various stations. 



This is probably a geographical form of Hesione splendida, Savigny, which is 

 characterised by the possession of one pair oi frontal antenna? ; eight pairs ot 

 tentacular cirri ; sixteen pairs of uniramous parapodia ; four distinct eyes ; pigment 

 disposed more or less in longitudinal bands or streaks. Savigny was in error regard- 

 ing the minute antennae, and the illustrations do not correspond with the text in 

 certain particulars, hence confusion has arisen. 



The Ceylon specimens range in length of body from 9 millims. to 3G millims. ; in 

 the latter case the ventral width between the parapodia is 4 millims., over the setae 

 11 millims. In all cases the full number of setigerous segments, namely 16, is 

 present. The extruded proboscis shows a median dorsal callosity or hard papilla 

 (not seen in the smallest specimen) a short distance from the base, like that figured 

 by Audouin and Milne-Edwards (1834) in 11. pantherina. The compound 

 falcigerous setae have bidentate appendices with a spiniform guard arising below 

 the denticulations. The guard may be worn away. 



A specimen of 14 millims. length had a ventral width between the parapodia 

 of 2 millims., over the setae nearly 5 millims. 



