46 THE AUSTRALIAN MUSEUM. 



unusually small (fig. 2), and leave wide transverse vessels which contain 

 muscle fibres. The meshes are occasionally sub-divided by a narrow 

 horizontal membrane, which does not interrupt the stigmata. 



The dorsal lamina is very slightly developed in this and some other 

 species of Polycarpa. It is quite narrow, and occasionally seems to almost 

 die away. The dorsal tubercle extends up to the bases of the tentacles, 

 but is simple in form (fig. 3). The intestine leaves a wide open loop 

 (fig. 4) which is occupied by a pad of gelatinous connective tissue. The 

 polycarps (figs. 4 and 5) are very numerous, but are not at first 

 conspicuous, as they are imbedded in the thick and rather tough mantle, 

 which is divided up by grooves into rudely quadrangular areas on its 

 inner surface. There may be 10 to 20 polycarps in each such area, and 

 each polycarp is of globular form like a little rounded sac with either one 

 or two spout-like ducts (see fig. 5). 



* 



Polycarpa Sluiteri, n. sp., PI. Cyn. IV., fig. 1, P 1 - ; 

 and PL Cyn. XVII., figs. 6-9. 



External appearance. Shape ovate, attached along the dorsal edge 

 and part of both sides. Posterior end rounded, no lateral compression. 

 Branchial aperture at the anterior end, atrial one-third down the dorsal 

 edge ; both on short rounded projections. Surface even, but finely 

 roughened all over by encrusting sand grains. Colour dark greyish 

 brown. Length 5'5 cm., breadth 3 cm., thickness 2-5 cm. 



Test thin, but stiff, brittle ; with sand grains imbedded throughout. 



Mantle very thin, adhering closely to test ; scarcely muscular at all. 



Branchial sac with 4 rather narrow folds. Each fold has 10 internal 

 longitudinal bars, and there are 8 in the interspace. The meshes are 

 square, and contain each 4 to 6 large stigmata regularly crossed by a 

 narrow horizontal membrane. 



Dorsal lamina a narrow plain membrane, rather curled round to form 

 a canal. 



Tentacles 8 large, 8 smaller, and about 16 very minute, arranged 

 regularly. 



Dorsal tubercle simple U-shaped, with both horns turned slightly in. 



Gronads numerous small polycarps (separate ovaria and spermaria) 

 imbedded in the mantle, and having long slender ducts. 



Locality. Port Jackson, on Ascidia phallusioides ; one specimen. 



This is a stiff-tested species (PL Cyn. IV., fig. 1, P 1 ') somewhat like 

 Polycarpa rigid a, but differing from that species in structure. The single 

 specimen occurs united in one mass with a large specimen of Ascidia 



