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



The Test is soft and cartilaginous. It varies greatly in thickness, as it is thin on the 

 anterior half, and then hecornes thicker, while the posterior third is a solid mass of test 

 suhstance. 



The Mantle is thin; the musculature is rather feeble; the siphons are very wide. 

 There are long, thin calcareous spicules found in the mantle. 



TJie Branchial Sac has eleven folds on each side. There are eight internal longi- 

 tudinal bars on a fold, and four in the interspace. The transverse vessels are mostly of 

 the same size, but here and there a much larger one occurs. The meshes are slightly 

 elongated transversely, and contain each about five stigmata ; they are generally divided 

 by delicate horizontal membranes. 



The Dorsal Lamina is formed of short blunt membranous languets. 



The Tentacles are branched ; there are nine large and nine small placed alternately, 

 and about eighteen very minute intermediate ones. 



Tlie Dorsal Tubercle. — The general outline is nearly circular, but considerably con 

 voluted. Both homs are turned inwards, and slightly coiled. 



This curious species has very much the appearance of an Ascidia, except that both 

 the apertures are more or less square (PL XVII. fig. 1). The test is cartilaginous, and 

 is very thick and solid at the posterior end. It contains quantities of short rod-like 

 calcareous spicules (PI. XVII. figs. 2 and 3). The spicules in the mantle (PI. XVII. fig. 4) 

 are like those found in Cynthia pallida, Heller, but are longer and thinner. They lie in 

 the interior of long membranous tubes or sheaths (PI. XVII. figs. 4, 5, and 6) which run 

 in zig-zags in all directions through the mantle. The spicules seem to fit the sheaths 

 exactly (fig. 6), and the echinations are placed in regular transverse rows. 



The branchial sac has a large number of folds (22), and they are all well developed 

 and have a number of internal longitudinal bars. The interspaces between the folds 

 (PI. XVII. fig. 7) are rather narrow, and have only four rows of meshes. 



Occasionally very wide transverse vessels are found (PI. XVII. fig. 7), but the others 

 are all of one size. Small fusiform and curved spicules are found scattered chiefly through 

 the transverse vessels. Two of them are represented more enlarged in PL XVII. fig. 8, 

 to show the arrangement of the spines in regular transverse rows. The curiously con- 

 voluted dorsal tubercle is shown in PL XVII. fig. 9. 



One specimen of this species was found at Port Jackson, Australia ; depth, 6 fathoms. 



Cynthia hisjrida, Herdman (PL XV. figs. 1-4). 



Cynthia hispida, Herdmau, Prelim. Rep., Proc. Roy. Soc. EdLn., 1880-81, p. 61. 



External Appearance. — The body is ovate or irregularly circular in shape ; it is flat- 

 tened laterally, and is nearly as broad as long ; the dorsal and ventral edges are strongly 

 convex ; the anterior end is broadish, and straight, and the body is attached by the 



