REPORT ON THE TUNIC ATA. G7 



The presence in this species of echinated ridges, terminating posteriorly in spines, 

 shows some resemblance to Salpa hexagona, but the two species differ in many points 

 — notably in the musculature. The distribution of the present species is wide. It was 

 taken twice in the Pacific and twice in the Atlantic. It appears to be identical \\i\X\ 

 the species found on the east coast of North America, which is sent out under the name 

 of ''Salpa (large species)" by the United States Fish Commission. 



A noteworthy point in regard to the shape is the bulb-like swelling of the posterior 

 part of the body (PI. V. figs. 1-3). It is seen in all the specimens. The narrow 

 anterior half of the body is almost cylindrical, and it terminates in a smooth, rounded, 

 anterior end. The posterior extremity, on the other hand, is irregularly pointed, and 

 bears the atrial aperture. The dorsal surface is flattened, and even slightly depressed, 

 while the sides of the body are rounded (PI. V. fig. 3). The ventral surface attains its 

 greatest convexity about two-thirds of the way back (PI. V. fig. 2). The longitudinal 

 serrated ridges are arranged as follows : — 



There are two main dorsal ridges which spring from the pointed posterior end, and 

 rapidly diverge until they are about 8 mm. apart on the wide bulbous part of the 

 body (PL V. fig. 1) ; they then approach slightly, and again diverge so as to attain a 

 lateral position, which they preserve until they gradually die away on the anterior end 

 of the body. Between these main dorsal ridges there are other shorter and less 

 conspicuous ridges on the dorsal surface, — one on each side of the middle line on the 

 posterior wider part of the body, and two on each side of the middle line on the 

 anterior narrower part of the body (PL V. fig. 1). There are also a few scattered 

 minute pointed tubercles between these ridges. Along each side of the body, rather 

 nearer the ventral than the dorsal surface, runs a well-marked longitudinal serrated 

 ridge. Its course is fairly straight (PL V. fig. 2). It is most strongly marked at the 

 posterior end, and dies away anteriorly. Finally, in the median ventral fine, on the 

 wider posterior end of the body, there is a strongly-marked longitudinal serrated ridge 

 (PL V. fig. 3). About 1'2 cm. from the posterior end this ventral ridge bifurcates, and 

 the two branches, which diverge slightly, run forwards till they die away on the 

 anterior extremity of the body. All these ridges are more conspicuous on the 

 posterior part of the body, and end posteriorly in prominent spines. There are thus 

 five main ridges (two dorsal, two lateral, and a ventral), and two slighter ones, on the 

 posterior half of the body ; and six main ridges (two dorsal, two lateral, and two 

 ventral), and four slighter ones, on the anterior half (see the transverse sections of the 

 anterior, fig. 6, and of the posterior, fig. 5, parts of the body showing the shape and the 

 arrangement of the ridges). 



The test of the anterior half of the body is very weak, posteriorly it is much 

 firmer, and over the region of the nucleus it becomes considerably thickened. The 

 edges of the small semicircular branchial aperture (PL V. fig. 1) are also thickened so 



