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



japonica the atrial aperture is situated on the dorsal edge, only about one-third of the dis- 

 tance from the anterior to the posterior end, while in Corella eumyota it appears from 

 Traustedt's figures to be about half-way down. In Corella japonica the musculature is 

 very strongly developed along the dorsal part of the left side (PI. XXVI. fig. 2, m.b.), 

 while in Corella eumyota there is no such disproportionate development. The two species 

 differ again in the structure of the branchial sac, as Traustedt's figures show a more 

 irregular arrangement of the sjiirals than that found in Corella japonica. 



The delicate branched processes of the test (PL XXVI. fig. 1 ) suggest the very similar 

 structures so well known in the Molgulidae, and in this case also sand grains are frequently 

 found adhering to or entangled in them, though never in any quantity. 



The very remarkable muscle bands seen in the mantle, especially on the left side just 

 below the siphons (PI. XXVI. fig. 2, m.b.), have a considerable resemblance to those found 

 in Abyssascidia wyvillii, and are even thicker than in that species. In some places they 

 terminate very abruptly (PL XXVI. fig. 6), their wide ends breaking up into a number 

 of short thick pointed processes, which rapidly taper off to a fine extremity. The ocelli 

 round the apertures are distinct. They are of a rust-red colour, and appear ring-shaped, 

 possibly from the presence of a light yellowish spot in the centre of the red. 



The branchial sac has the structure usually found in Corella ; the transverse vessels 

 and the longitudinal tubes connecting them are wide, while the internal longitudinal bars 

 are very narrow, and are more numerous than the rows of spirals (PL XXVI. figs. 4 and 5). 

 The horizontal membranes are wide, and are very numerous. They have frequently 

 curved prolongations or connecting ducts which join the internal longitudinal bars in 

 certain positions. These look as if they projected from the bars, and thus they gave rise 

 to the erroneous statement in the description of this species in the Preliminary Report, 

 that the internal longitudinal bars are provided with long curved papillae. One other 

 point in regard to the branchial sac must be noticed. In some places the internal 

 longitudinal bars are very much broken up, as seen in figure 8. A bar may end csecally 

 close to its point of attachment to a horizontal membrane, and may begin again at the 

 next membrane, leaving a gap between the two ; it may then continue normally, or it 

 may terminate again, in which case there will be a short piece of generally curled tube 

 ending csecally in both directions, and attached by the middle to a horizontal membrane 

 (PL XXVI. fig. 8). This irregularity in the internal longitudinal bars may also be 

 observed in Corella parallelogramma of our own coasts. 



The languets along the dorsal edge of the sac are narrow and tapering ; they are all 

 of the same size, and are not placed closely (PL XXVI. fig. 7, /.). The tentacles are 

 very closely packed, and are apparently all of the same size. The symmetrically-shaped 

 dorsal tubercle (PL XXVI. fig. 9, d.t.) lies in a shallow triangular peritubercular area, 

 and is separated by less than half its own height from the bases of the tentacles. 



The viscera are in the position usual in the genus, namely, on the right side of the 



