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



as to form a distinct margin. The atrial aperture has no bounding margin except the 

 spinose processes which terminate the longitudinal ridges posteriorly. 



The measurements given above are taken from the specimen obtained on 

 November 5, 1875. The two specimens collected on October 21, 1875, are larger, and 

 measure 5 '5 cm. and 4 "2 cm. in length. The two specimens from Station 314, January 

 21, 1876, measure 3'7 cm. and 5 cm. in length. The remaining specimen, collected on 

 April 12, 187G, is 3 cm. in length. 



The muscle bands in the mantle are rather narrow, and are all of much the same 

 size. There is no musculature on the ventral surface, as all the bands end on the sides 

 of the body (PI. V. fig. 2). The musculature of the dorsal surface (PL V. fig. 1) is 

 somewhat like that of the solitary forms of Sa^^a runeinata-fusiformis and of Salpa 

 cylindrica, but differs from both. In Salpa runcinata the eighth and ninth bands 

 approach and meet dorsally, and in Salpa cylindrica the fourth band joins with the first, 

 second, and third dorsally ; while in the present species the fourth, eighth, and ninth 

 bands are quite distinct and independent of their neighbours. Figure 7 shows the 

 junction of the first, second, and third bands dorsally. 



The conspicuous endostyle (PL V. figs. 3 and 9, en.) is of a slightly yellow* colour. 

 In the specimen collected on November 5, 1875, it is 3 cm. in length, and extends from 

 close to the anterior end of the body (1 mm. in front of the peripharyngeal band) to the 

 anterior part of the visceral mass. The peripharyngeal bands bend posteriorly on the 

 sides of the body and on the dorsal surface (PL V. fig. 9, p-P-), so that the dorsal 

 tubercle comes to be placed posterior to the anterior extremity of the endostyle. 



The nerve ganglion is small and of rounded form. The dorsal lamina is fairly large. 

 The transverse ridges on it are rather wide, closely placed, and arranged with great 

 regularity (PL V. fig. 8). Their- course is almost straight. The dorsal tubercle has a 

 curved free margin (PL V. fig. 9, d.t), with rounded anterior and posterior ends. The 

 languet is not well marked. 



The visceral mass is formed of two parts, of which one is globular in shape, and is 

 composed of the alimentary and reproductive vLscera ; while the other is of curved or 

 irregularly crescentic shape, and is probably the remains of the elasoblast (PL V. 

 figs. 3, 4, and 10). Figure 4 also shows, placed more anteriorly in the median ventral 

 line, a spherical dark-coloured mass, which may be what is left of the " placenta " of 

 the embryo. In that case the specimen figured is of course a solitary form, although it 

 shows no trace of a developing chain. 



Scdpa mollis, n. sp. (PL V. figs. 11-15). 



External Ap>pearance. — The shape is elongated, and sub- cylindrical. The anterior 

 and posterior ends are moderately wide, and the sides are nearly parallel. The 



