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



The Tentacles are simple, they are stout and rather curled, about thirty in number 

 and all of much the same size. 



Tlie Dorsal Tubercle is simply oval; the aperture is at the narrower anterior end; the 

 horns are not coiled, and nearly touch. 



This is an ordinary and typical Styela, except that the apertures are not clearly 

 four lobed, but seem to have one or two extra projections each (PI. XIX. fig. 3). The 

 mantle and test are closely united; both are thin but strong, the test being in the 

 typical Cynthiad condition — namely, tough and leathery. 



The branchial sac is normal. The eight folds are well marked, and the vessels and 

 meshes are of an ordinary size (PI. XIX. fig. 4). Two sizes of transverse vessels were 

 noticed, but they do not seem to alternate regularly. Besides these, a delicate 

 horizontal membrane appears to be invariably present, cutting each mesh into two areas 

 (PI. XIX. fig. 4, tr.'). 



One specimen of this species was obtained in the Antarctic Ocean, to the south of 

 Kerguelen Island, at Station 150; February 2, 1874; lat. 52° 4' S., long. 71° 22' E.; 

 depth, 150 fathoms; bottom temperature, l° - 8 C. ; bottom, rock. 



Styela lactea, Herdman (PI. XIX. figs. 7-8). 



Styela lactea, Herdman, Prelim. Rep., Proc. Roy. Soc. Edin., 1880-81, p. 68. 



External Appearance. — The body is nearly rectangular, varying from an oblong to 

 a spherical shape ; it is erect and not compressed. The anterior end is straight and wide, 

 the posterior end is also straight and is nearly as wide. The dorsal and ventral edges are 

 slightly convex. The body is attached by the whole of the posterior end. The apertures 

 are both anterior ; they are nearly sessile, and are four-cleft. The branchial is at the 

 ventral edge of the anterior end, and is directed ventrally ; the atrial is at the dorsal edge 

 of the anterior end, and is directed anteriorly and dorsally. 



The surface is smooth, but is seamed with transverse creases and slight folds, while 

 longitudinal ones are seen here and there. The colour is a creamy white. 



Length of the body, 4"5 cm.; breadth of the body, 3'5 cm. 



Tlie Test is thick, but soft and flexible ; it is quite opaque. 



TJie Mantle is closely attached to the test. The musculature is fine, and is composed 

 of longitudinal and transverse bands intersecting at right angles. 



The Branchial Sac has four folds upon each side. The internal longitudinal bars are 

 rather few, but wide ; there are about six on a fold, while they are few and distant in the 

 interspaces. The meshes are greatly elongated transversely, some of those near the 

 endostyle containing thirty or forty stigmata ; they are occasionally divided by narrow 

 horizontal membranes. 



The Dorsal Lamina is a plain membrane, with no ribs, and an even margin. 



