REPORT ON THE TUNIC ATA. 85 



The length is about 1 cm., and the greatest breadth about 8 mm. 



The Test is clear and transparent. It is moderately thick and firm. 



The Mantle has a very slight musculature. There are only four short muscle bands, 

 and they are arranged so as to form two small X'Shaped figures on the dorsal surface, 

 one near the anterior and the other near the posterior end. 



27)6 Endostyle is rather short and curved. It extends from the branchial aperture 

 about half-way to the posterior end of the body. 



The Dorsal Lamina consists of a short and club-shaped anterior part, which is not 

 attached at its posterior end, but hangs freely in the branchial cavity, and a smaller 

 posterior part close to the oesophageal aperture. It is strongly ribbed transversely 

 throusfhout its length. 



The Dorsal Tubercle has an antero-posteriorly elongated double groove with the 

 opening at the posterior end. There is also a languet-like projection at the anterior end. 



The Visceral Mass is of large size, and is placed posteriorly and ventrally. 



Zoca%.— April 13, 1876 ; Station 352, North Atlantic; lat. 10° 55' 0" N., long. 

 17° 4G' 0" W. ; surf. temp. 77°-7. 



A single specimen of this curious form was obtained in the North Atlantic, oflP the 

 West Coast of Africa, in the surface tow-net. In general appearance (PI. IX. fig. 1) it 

 is rather unlike a Salpa, being short, and wdde dorso-ventrally, but narrow from side to 

 side. On discovering the remarkable condition of the dorsal lamina, I was at first 

 inclined to separate this form from Salpa as the type of a new genus, but 1 liave 

 decided not to take this step on the strength of the single specimen, in case of the short, 

 free, club-shaped dorsal lamina (PI. IX. figs. 4, 6) being merely au individual 

 abnormality. Of the known species of Salpa this form approaches most nearly to the 

 solitary generation of Salpa scutigera-confoederata, but difi"ers from it in shape and 

 many minor details in addition to the dorsal lamina. 



The test is not thickened over the visceral mass. The musculature of the mantle is 

 even slighter than that of Salpa scutigera-confoederata, but is arranged in the same 

 manner so as to form two X'^^'^'P'^f^ marks in the median dorsal line (PI. IX., 

 compare figs. 1 and 9). The anterior X is placed close behind the nerve ganglion 

 (PI. IX. figs. 2, 3, 4, m.h.), while the posterior one (PI. IX. fig. 5) is near the 

 atrial aperture. The branchial aperture is crescentic with slight lips (PI. IX. figs. 

 1, 2, 3), while the atrial is a transverse slit with a slightly lobed margin 

 (PI. IX. fig. 5). 



The course of the endostyle is shown in fig. 1. It curves first ventrally and then 

 posteriorly, and is continued back from where it stops, about the middle of the body, to 

 the visceral mass by a fold of the ventral wall of the branchial sac. There is a distinct 

 break or gap betw-een the extremity of the endostyle and this fold (PI. IX. fig. 7). 



