298 BULLETIN OF THE 



The test (Figs. 1, 2, and 3, a) is very thick, and, in our species, so per- 

 fectly transparent that its outline can be traced only when the animal is 

 seen strongly illuminated upon a dark background. The branchial aper- 

 ture is at the anterior end of the body of the solitary form (Figs. 1, 2, e), 

 although the test of the chain-Salpa (Fig. 3) projects some distance in 

 front of it, upon the haemal side ; in both the test extends posteriorly 

 beyond the atrial aperture g. In the young of both forms the latter open- 

 ing is much nearer the branchial than in the adults, and in this respect 

 the young Salpa resembles the adult of the ordinary fixed ascidians. The 

 shape of the test varies greatly in the diffei'ent species, as well as in 

 the two forms of the same species. The solitary form of our species,* 

 when seen from above or from below (Fig. 2), is barrel-shaped in out- 

 line, with the posterior extremity obtusely pointed and the anterior 

 truncated. At the sides of the posterior extremity the test is pro- 

 longed so as to form two long, slightly curved processes, each of which 

 contains a coecum of the outeriunic, with a cavity which is continuous 

 with the sinus system. When seen in profile (Fig. 1), it is truncated 

 at both ends, from the neural to the haemal side ; the extremities are 

 slightly convex ; the posterior truncating plane is more inclined than 

 the anterior. Besides the two large posterior processes there are six 

 much smaller ones, two on the median line and two pairs, all of which 

 are composed of the test only, with no inner chamber. The anterior 

 opening for the admission of water (Figs. 1, 2, 3, e) is by far the 

 larger ; it occupies the whole width of the body, while the posterior 

 one (<j) through which the water is expelled is much narrower, and 

 placed at a short distance from the posterior extremity, at the base of 

 the truncating plane, on the neural side ; the anterior opening being 

 nearer the haemal side. The lips which close these openings are quite 

 prominent, and can be thrown considerably beyond the general out- 

 line, either when drawing in water or forcing it out. 



Since the Chain-salpce are normally united into a chain composed 



* This species is very abundant along the southern shore of New England, and was 

 described by Desor (Proc. Boston Soc. Nat. Hist., III. 184S, p. 75) as Salpa Caboti; 

 and subsequently figured ami described by A. Agassiz (op. cit. XI. p. 17) under the 

 same name. It seems to agree, in all respects, with the Salpa spinosa, Otto, figured 

 and described by Sars (Fauna littoralis Norvegine, 1S46, p. 85, Tab. 10, Figs. 1, 2. and 9). 

 The Salpa spinosa of Otto is stated to be the same as the S. mucronata-democratica of 

 Forskfd, but as I have not been able to see Forskal's figures, I am unable to tell from 

 his description whether the American species is the same. 



