yS RITTER. [Vol. II. 



from the vicinity of the Scandinavian peninsula. The addition 

 of these species to the others already known from far northern 

 seas increases quite to a certainty the probability that there 

 is a distinct Arctic tunicate fauna. The clearest indication of 

 this is afforded by the presence in the collection of the species 

 of the genera Dcndrodoa and Syiioiciivi. The single species 

 of the first-mentioned genus hitherto known was described 

 by MacLeay in 1824 from Winter Island (north of British 

 America). Herdman has expressed doubt as to whether or 

 not MacLeay's genus is really distinct from Styela. From 

 the two species now at hand I have convinced myself that 

 the genus is thoroughly valid — much more so than many 

 others that receive general recognition. This, then, appears 

 to be one characteristically Arctic genus. The other genus 

 above mentioned, Syiioiciim, seems to be quite as character- 

 istically Arctic. The first species belonging to it was made 

 known by Phipps (1774), and more fully described by Savigny 

 in 1 8 16, and came from Spitzbergen. Since then another 

 species from Lofoten Islands, north coast of Norway, has 

 been described by Sars. This, then, seems to be another 

 genus characteristically northern. 



Of the other species the one belonging to the genus Apli- 

 diopsis has its nearest ally in A. sarsii Huitfeldt-Kaas, from 

 Lofoten ; and two of the three species of Amaroitciimi appear 

 to be more closely related to A. mutable Sars, from Hamer- 

 fest, Norway, than to any other member of this large genus. 

 The one representative of the genus Boltenia I identify as 

 B. elegants Herdman, from the north Atlantic ; so that six 

 of the eleven species may be said to be characteristically 

 far northern, three of them very pronouncedly so, they 

 belonging to genera that are exclusively of this character. 

 The genera Polyclinum and Ainai'oiicimn are both cosmo- 

 politan in their distribution ; they are almost sure to be 

 represented in any considerable collection of compound 

 ascidians from any part of the world, so that it is only by 

 comparing among themselves the different species in each 

 genus that anything significant as to distribution can be 

 learned. 



