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



The Branchial Sac is delicate. The internal longitudinal bars are narrow but distinct ; 

 they are undulating, and are supported by broad horizontal membranes, provided with 

 triangular flaps, to the apices of which the bars are attached. There are no papillse. The 

 transverse vessels are narrow, and all of one size. The meshes are regular, elongated 

 antero-posteriorly, and contain each about three long and regular stigmata, with parallel 

 sides and rounded ends. 



TJie Dorsal Lamina is represented by a series of long narrow languets, with undula- 

 ting edges, and tapering to a fine point. 



The Tentacles are filiform, few, and distant. 



The Dorsal Tubercle is irregularly oval in outline. 



Tlie Viscera are prolonged beyond the branchial sac posteriorly, and extend into the 

 narrow posterior part of the body. 



This is a strong and moderately large species (PI. XXXVI. fig. 7). The individuals 

 or Ascidiozooids are united by a short rough stolon, which is merely a prolongation of 

 their posterior ends. On this stolon the test is very thick and strong ; while over the 

 anterior part of the body it is usually thinner ; in one individual the dark-brown longi- 

 tudinally running muscle bands of the mantle show through distinctly. The posterior 

 part of the body, into which the intestine is prolonged, is much narrower than the anterior 

 or branchial region. The apertures are both near the anterior end, and are not far apart. 

 They are sessile, but distinct, and are lobed, though usually only indistinctly and irre- 

 gularly. When most distinct, the lobes seem to be six round the atrial aperture and 

 seven or eight round the branchial. 



The appearance of the mantle is rather characteristic, the dark reddish brown muscle 

 bands showing very distinctly as fine distant lines on the thin membrane. 



The branchial sac (PL XXXVI. fig. 8) is rather like that of Ecteinascidia crassa ; it 

 differs from it chiefly in the stigmata being longer, while the transverse vessels are 

 relatively narrower, and in having the large triangular connecting ducts or flaps of the 

 horizontal membranes shorter and placed rather further apart (PI. XXXVI. figs. 8 and 

 13). In Ecteinascidia crassa the points of these flaps, when laid down on the sac (fig. 13), 

 extend past the tops of the stigmata of the next row, while in the present species they 

 only extend three-quarters of the way down the stigmata of their own row (fig. 8). 

 In consequence of the length of the stigmata, the meshes in the present species are 

 elongated antero-posteriorly, while in the Ecteinascidia crassa they are square (compare 

 figs. 8 and 13, PI. XXXVI. ). The stigmata are usually very regular, with rounded 

 ends. Figure 9 shows a slight irregularity which was noticed. 



The languets in this species are long and narrow, tapering gradually to a point. When 

 stretched out, each overlaps the succeeding one by about half its length (PI. XXXVI. 

 fig. 11, I.). They are arranged down the centre of a wide membranous area which runs 



