REPORT ON THE TUNICATA. 225 



The branchial aperture is so damaged in both specimens that it is impossible to make 

 out the exact number of tentacles and the condition of the dorsal tubercle. 



Two specimens, both more or less injured, were obtained off East Moncceur Island, 

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



Pachychlama gigantea, Herdman (PL XXVIII. figs. 6-11, and PL XXIX. fig. 10). 

 Pachychlcena gigantea, Herdman, Prelim. Rep., Proc. Roy. Soc. EJin., 1879-80, p. 463. 



External Appearance. — The shape of this species, as far as can be made out, is 

 irregularly oblong, the right side being larger than the left. Probably the body is 

 attached by the posterior part of the ventral edge. The branchial aperture is eight-lobed, 

 terminal, and placed on a large irregularly rounded projection turned towards the left side 

 The atrial aperture is six-lobed, and is also on a large projection, situated on the dorsal edge ; 

 from one-third to half-way down from the anterior to the posterior end. The lobes of 

 both apertures are irregular, but prominent. 



The surface is very irregular, and in some places is almost covered by foreign bodies. 

 The colour is a warm yellowish-grey. 



Length of the body, about 12 cm.; breadth of the body, 5 to 7 cm. 



TJw Test is cartilaginous, very thick (varying from 2 mm. to 4 cm.), solid, rigid, and 

 opaque ; it is white in mass with a hyaline tint where thin, and yellowish -grey on the 

 external surface. Large vessels ramify in the inner laj^er ; the vascular trunks probably 

 enter the test at the base of the right side towards the ventral edge. The terminal twigs 

 of the vessels are sometimes slightly swollen, but scarcely knobbed ; in some places they 

 are almost covered by bundles of rod-like or tapering yellowish crystals. The bladder 

 cells are very small, and are abundant in the outer part of the test around the small 

 vessels, where yellow pigment cells are also present. 



The Mantle is strongly muscular over the right side and on the siphons, while on the 

 left side it is membranous. In several places, especially between the siphons and at the 

 anterior extremity of the endostyle, it is marked with dark red. 



The Branchial Sac is very thick, coarse, opaque, and of a brown colour. It is longi- 

 tudinally plicated, and has the grooves broken up into pouches by the larger transverse 

 vessels. On the external aspect of the sac certain very wide transverse vessels are 

 connected by equally wide, irregularly placed longitudinal vessels, thus forming an 

 external network of quadrangular meshes, each of which contains about four rows of 

 stigmata. The internal longitudinal bars are stout and bear strong conical papillae. The 

 meshes are much elongated transversely, and each contains twelve to twenty stigmata. 



TJie Endostyle is not conspicuous, it is yellowish, with a dark red line down each side. 



Tli e Dorsal Lamina is wide, and is strongly ribbed transversely, but not pectinated. 

 It becomes wider and thinner as it approaches the oesophageal aperture, and then narrows 

 again rapidly after passing it. 



