178 THE VOYAGE OF H.M.S. CHALLENGER. 



continuous at the apex (PL XXIII. figs. 5 and 6). The polycarps are numerous and 

 large, and of a yellow colour. 



Three specimens of this species were found at Port Jackson, Australia, in from 6 to 15 

 fathoms. 



Polycarpa irregularis, Herdman (PL XXIII. figs. 7 and 8). 



Polycarpa irregularis, Herdman, Prelim. Eep., Proc. Eoy. Soc. Edin., 1880-81, p. 72. 



External Appearance. — The body is irregularly oblong, somewhat pyriform, erect, 

 and rather compressed laterally. The anterior and posterior ends are narrow, and the 

 middle two-fourths are wide, and have the dorsal and ventral edges parallel ; the ventral 

 edge is straight throughout ; the dorsal slopes in its anterior and posterior fourths, but is 

 straight in its central two-fourths. The body is attached by the narrow but irregular 

 posterior end. The branchial aperture is terminal and prominent, and is surrounded by 

 four large lobes and four small ones ; the atrial is on the dorsal edge, rather more than 

 one quarter of the way down ; it is distinct. 



The surface is very irregular ; it is cut up by deep grooves and folds, and is partially 

 covered by foreign bodies. The colour is a dirty yellowish-white. 



Length of the body, 6 cm. ; breadth of the body, 3"5 cm. 



The Test is rather thick and tough ; it is white and glistening on the inner surface. 



The Mantle is thin, and the musculature is not strong. 



The Branchial Sac has four folds upon each side. There are two or three narrow 

 transverse vessels between each pair of wider ones. About eight internal longitudinal 

 bars are present on the folds, and twelve in the interspaces. The meshes are transversely 

 elongated, and contain each six stigmata. 



The Dorsal Lamina is narrow and smooth. 



The Tentacles are linear and rather distant ; they are twenty-four in number, and are 

 coloured black ; some are rather smaller than the others, but are not placed alternately. 



The Dorsal Tubercle is ovate in shape, but has the narrow end placed posteriorly ; it 

 is much convoluted and marked with black. 



The surface of this large Polycarpa is curiously irregular (PL XXIII. fig. 7), especially 

 at the posterior end. The test is thick and tough, and of a yellowish-white colour. The 

 apertures are both distinct. The branchial has eight lobes, but four of them are large, 

 while the others are merely intermediate smaller processes or folds. 



In the branchial sac there are two distinct sizes of transverse vessels. Each pair of 

 larger ones is separated by either three or, more rarely, two smaller ones (PL XXIII. 

 fig. 8). The stigmata are small, and show a considerable amount of irregularity. 

 Horizontal membranes are not much developed. 



