288 CEYLON PEARL OYSTER REPORT. 



eleven following segments are biannulate and carry dorsal and ventral fascicles of 

 capillary setae. The unciniform seta? commence on the 14th segment, the dorsal 

 torus containing a single row of 19 setse, the ventral torus a single row of 34 

 (Plate V., fig. 119). From the mouth projects a median tongue-like lobe. The. head 

 is half withdrawn into the buccal segment, but by pressing the latter backwards ac 

 acervus of eye-spots at the side of the head can be seen (Plate V., fig. 118). 



Family: OPHELILD.E. 

 Armandia lanceolata, n. sp. Plate V., fig. 120. 



Locality : South of Manaar Island, 8 to 9 fathoms. 



One specimen about 17 millims. in length ; 29 pairs of parapodia, the last three or 

 four of which are very small ; 22 pairs of cirriform branchiae commencing on the 2nd 

 setigerous segment ; eleven pairs of lateral eyes situated in front of the jwapodia 

 from segments VII. to XVII. inclusive ; no cephalic eyes observed. This is a slender 

 worm 1 millim. in diameter ; body pale. 



Ophelioids of this group show a striking resemblance to Amphioxus in shape, size, 

 habits, distribution, consistency, translucency, and movements. This has been 

 remarked previously by Lo Bianco (1893) in the case of Armandia polyopldhalma 

 and by me (1896) in New Guinea waters.* Although infinitely removed from each 

 other in morphology, Armandia and Amphioxus are closely approximated in bionomics. 

 It is a case of true homoplasy ; there is no question of affinity, nor of mimicry, nor of 

 parallel evolution. 



The ventral musculature in this species is so arranged as to cause two prominent 

 longitudinal ventro-lateral ridges, like metapleural folds, extending uninterruptedly 

 from the mouth to the base of the anal siphon, leaving a narrow deeply depressed 

 median ventral tract, the neural groove, between them ; and a lateral groove above 

 on each side of the body in which the parapodia lie. The branchiae can be kept 

 lengthwise lodged within the lateral groove. The anal siphon is a narrow mem- 

 branous tube terminating in a circular orifice fringed by not less than 12 subulate 

 papilla?, subequal. 



In Armandia leptocirrus, Grube ('Ann. Semp.,' p. 194) there are 33 pairs of gills, t 

 a pair to each of 34 segments excepting the first ; the lateral eyes are said to 

 commence on the fifth setigerous segment and to occur on the ten following segments. 

 Sometimes the eyes may be absent or lost from some of the ommatophorous segments. 

 In this specimen of A. lanceolata they are complete on the right side, but on the left 

 side missing from the 11th to 13th segments. The first eye occurs on the 7th 

 setigerous (6th branchiferous) segment, the last on the 17th setigerous (16th 

 branchiferous) segment. The anal siphon has a marked ventral flexure in the 



* Cav. Lo Bianco, 'Atti Ace. Napoli,' v., 1893; A. Willey, 'Quart. Journ. Micro. Sc.,' vol. 39, 

 August, 1896, p. 219. 



t Given as 22 pairs by a misprint. 



