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



Heller, in his diagnosis of Styela, states that the dorsal lamina has a smooth edge ; 

 but this species, which is undoubtedly a Styela in all its other characters, has a series of 

 short tapering languets along the dorsal line of the sac. Another new species (Styela 

 Jlava) has the dorsal lamina ribbed transversely, and slightly pectinated at the margin, 

 evidently a condition intermediate between that seen in Styela bythia and that found in 

 other members of the genus. Hence I had no hesitation in changing the characters of 

 the genus slightly, so as to admit of the reception of Styela bythia. 



It is a compact, irregularly hemispherical species, and was dredged from 2600 fathoms, 

 attached to a manganese nodule, along with a specimen of Styela squamosa (PI. 

 XVIII. fig. 1. The lower specimen on the nodule is Styela bythia). The test is thick 

 and stiff, but rather brittle. It adheres closely to the mantle below, but when detached 

 shows a white inner surface. 



The branchial sac (Pi. XVIII. fig. 6) looks rather thick and opaque. This appearance 

 is caused by the large number of internal longitudinal bars present. These are 

 broad and ribbon-like, and are so closely placed that the meshes between them usually 

 contain only one or sometimes two stigmata each (PI. XVIII. fig. 6). Otherwise the 

 branchial sac has no very notable features. The transverse vessels are all of the same size, 

 the meshes arc small and particularly narrow, and are all divided transversely and sym- 

 metrically by narrow membranes. Figure 7 on Plate XVIII. shows a small portion of the 

 sac from the outside and more highly magnified. The outline of the stigma is rather 

 irregular, and no cilia could be discovered in any part of the sac which was examined. 



The languets (PL XVIII. fig. 8, /.) are short but stout, and spring from a narrow, 

 transversely ribbed membrane (</./.) forming the basal part of the dorsal lamina. 



One specimen of this interesting species was dredged to the south of Australia, a1 

 Station 160; March 13, 1874; lat. 42° 42' S., long. 134° 10' E.; depth, 2G00 fathoms; 

 bottom temperature, 0° - 2 C. ; bottom, red clay. 



Styela squamosa, Hcrdman (PL XVIII. figs. 1-5). 



Styela squamosa, Herdmaa, Prelim. Rep., Proc. Roy. Soc. Edin., 1880-81, p. 66. 



External Appearance. — The body is roughly hemispherical, and is slightly compressed 

 laterally. The anterior end is very large, and rises somewhat towards its ventral 

 extremity; the ventral edge is nearly straight, while the dorsal is gently convex. The 

 body is attached by the wide posterior end, and the margin is slightly expanded. The 

 apertures are sessile, distant and inconspicuous. The branchial is at the ventral end, and 

 the atrial at the dorsal end of the anterior extremity. 



The surface is smooth but scaly. The colour is creamy white and slightly yellow in parts. 



Length of the body, 2 cm.; breadth of the body, 1*5 cm. 



'Ihe Test is thick and solid, but soft. 



Tlie Mantle is very thin, and adheres slightly to the test. 



