326 CEYLON PEARL OYSTER REPORT, 



of three sizes, arranged with regularity, and there may also he narrow horizontal 

 membranes crossing the stigmata (fig. 4). 



Dorsal Lamina a low plain ridge. 



Tentacles of two sizes, about 20 larger and the same number of smaller, placed 

 alternately (fig. 2). 



Dorsal Tubercle a large circular area with a small opening at one side, around it is 

 a swollen spongy area. 



Locality: Station XLIX., South-west of Cheval Paar, 13 fathoms, one specimen. 



This species is named in honour of the late Mr. Oliver Collett, an excellent 

 naturalist in Ceylon, much interested in the pearl oyster investigation. 



Polycarpa willisi, n. sp. Plate VI. , figs. 9 to 15. 



External Appearance. Elongated ovate, almost fusiform, with the large siphons 

 at opposite extremities of the body (fig. 9) ; each opening very distinctly four-lobed 

 and surrounded by a square rim (fig. 11). Surface sandy ; size, 1'4 centims. in length. 



Test thin, sparsely covered with adhering sand. 



Mantle opaque, pigmented with orange and pale yellow ; siphons long (fig. 10). 



Branchial Sac with four folds on each side. About five bars on each fold, and two 

 rows of meshes between. The stigmata (fig. 12) are very short, and rather irregular ; 

 they form ovate or rounded holes from two to four in a mesh. 



Dorsal Lamina a narrow plain membrane. 



Tentacles of three sizes arranged regularly (fig. 13), there being eight large, eight 

 medium, and sixteen smaller between. 



Dorsal Tubercle a rounded mass with no distinct horns (fig. 13). 



Alimentary Canal a narrow, short loop; stomach smooth, and coloured yellow. 



Gonads about 12 elongated orange-brown polycarps on each side of the endostyle 

 (tig. 14), and a number of more rounded pale lemon-yellow endocarps (tig 15) scattered 

 between. Each gonad has the ova in the centre and the testes placed around. 



Locality : Station LXIL, Periya Paar, 13 fathoms, three specimens of about the 

 same size. 



The interior of the body is much pigmented with opaque yellow, especially the 

 alimentary canal, the endocarps, and the mantle. 



I have pleasure in naming this species after my friend Dr. J. C. Wielis, Director 

 of the Royal Botanic Gardens at Peradeniya, Ceylon. 



Polycarpa twynami, n. sp. Plate VI., figs. 27 to 32. 



External Appearance. Body erect, oblong, attached by the rather narrower 

 posterior end. Branchial aperture anterior atrial a little way along dorsal edge, both 

 sessile (fig. 27). Surface somewhat corrugated and wrinkled. Colour, brown ; size, 

 3 '5 centims. x 1*5 centims. 



Test leathery but soft, and irregularly thickened, brown inside. 



Mantle opaque brown, adhering closely to the test. 



