vni.. 2, pt. 2.] A TAXONOMIC STUDY OF THE SALPIDAE METCALF. 9 



The Salpidae, other than the Cyclosdlpae, none of them form 

 whorls upon their stolons, and many of them show more or less 

 marked asymmetry in the aggregated individuals. This asymmetry 

 affects both the shape of the body and the arrangement of the muscles 

 in the aggregated Apsteinia asymmetrica and A. magalhancia. It 

 affects the arrangement of the muscles, but not the body form, in 

 the globose A. punctata. It affects the shape of the body and some- 

 what the arrangement of the muscles, especially those of the base 

 of the atrial siphon, in the aggregated forms of Ritteria amhoinensis 

 and R. Jiexagona, Salpa maxima and its variety tuberculata, S.fusi- 

 formis and its form aspera, and Iasis zonaria. The aggregated forms 

 of Salpa fusiformis and S. cylindrica are really asymmetrical in the 

 shape of the body and in the position of the atrial siphon and its 

 sphincter muscles, though the asymmetry is less marked in these 

 species. Thalia, Thetys, Traustedtia, and Pegea show little asymme- 

 try. Possibly a detailed study of the attachment of the individuals 

 in the stolon might throw light upon the absence of asymmetry in 

 these species, but we have not undertaken the study. 



CYCLOSALPA PINNATA I (Forskal) (1775). 



Thalia No. 1 and No. 2, No. 3 (?), Browne, 1756. 



Holoihuria thalia Linnaeus, 1758 [=Browne, Thalia No. 1]. 



R. caudata Linnaeus, 1758 [=Browne, Thalia No. 2]. 



Salpa pinnata Forskal, 1775. 



S. cristata Cuvier, 1804. 



S. caudata Lamarck, 1813. 



Dagysa [species not named] Home, 1814. 



Salpa thalia Lamarck, 1816. 



S. cyanea Delle Chiaje, 1828. 



S. proboscidialis Lesson, 1830. 



Cyclosalpa pinnata Herdman, 1888. 



Cyclosalpa pinnata is in some regards the most primitive of the 

 Salpidae. Its body muscles have a hoop-like arrangement in the 

 solitary form (pi. 1, fig. 1), and are interrupted both dorsally and 

 ventrally in the median plane. To those who believe with Brooks 

 that the Salps are descended from Doliolum-like ancestors, the regu- 

 lar hoop-like arrangement of the muscles would seem primitive and 

 their dorsal and ventral interruption secondary. Their regularity 

 of arrangement seems almost surely primitive. 



The bilateral symmetry of the aggregated zooids in this species, 

 and in the ether Cyclosalpae symmetricales, might at first thought 

 seem another archaic feature, but the accuracy of this suggestion 

 depends perhaps upon whether the habit of forming whorls of zooids 

 upon the stolon is primitive or secondary, for, as already noted, the 



i The identification of Browne's "Thalia No. 1" and " Thalia No. 2'' as Cyclosalpa pinnata, solitary and 

 aggregated forms, seems in all probability correct. However, as the identification is not beyond question, 

 it does not seem best to displace the long established species name pinnata, substituting the name thalia 

 winch Linnaeus gave, following Browne. 



