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



is terminal and projecting, while the atrial is on the dorsal edge, fully one-third of the 

 way from the anterior to the posterior end, and projecting. Both are very indistinctly 

 lobed. 



The surface is even but roughish, and partly covered by foreign bodies. The colour 

 is a dull greyish-brown, but dull yellow round the apertures. 



Length of the body, 8 cm. ; breadth of the body, 3 cm. 



TJie Test is not very thick and not tough, but is very stiff, like cardboard. It is white 

 on section and on the inner surface. 



The Mantle is thin, and adheres closely to the test; the musculature is feeble. 



The Branchial Sac has four folds upon each side. The transverse vessels are of two 

 sizes, about twelve narrow ones being placed between every two larger ones. There are 

 about twelve internal longitudinal bars on the folds, and six in the interspaces. The 

 meshes are transversely elongated, and contain twelve stigmata each. 



TJie Dorsal Lamina is a narrow plain membrane, with the edge even. 



The Tentacles are simple and closely placed ; they are stout, and about forty in 

 number, all of one length. 



The Dorsal Tubercle is oblong, lies in a very large triangular peritubercular area, and 

 is directed forwards and to the left. 



This is a very large species to belong to the genus Pohjcarpa. It stands erect, 

 attached by the posterior end, and having the branchial aperture uppermost (PL XXIII. 

 fig. 1). The test, though not thick, is very stiff, and has a few shell fragments and other 

 foreign matter adhering. 



The branchial sac is strong, and has very wide internal longitudinal bars (PI. XXIII. 

 fig. 2, i.l.). These are numerous, and form well developed folds. In the interspaces the 

 meshes are transversely elongated. The. larger size of transverse vessel is very wide, as 

 wide as one of the rows of stigmata. This sac is somewhat irregular in parts, and in two 

 places in the portion figured (PI. XXIII. fig. 2) the passage of one row of stigmata into 

 two rows is seen. In the middle of the lower edge of the figure some of the stigmata are 

 reduced to very small oval or rounded apertures. The tentacles are large, are all of one 

 length, and are crowded together. 



The intestine forms a very wide loop. The polycarps are deeply imbedded in the 

 mantle, and hence only project slightly. In the genital masses some of the mature ova, 

 which were incidentally examined, had each several distinct germinal spots. 



Two specimens of Polycarpa rigida were obtained off East Moncceur Island, in 

 Bass Strait, at Station 162 ; April 2, 1874 ; depth, 38 to 40 fathoms ; bottom, sand. 



