AN ENTOPROCTAN POLYZOON (BARENTSIA BENEDENl). 843 



I therefore refer Pedicellina gracilis, P. belgica, and Gonypodaria nodosa to 

 Barentsia gracilis (Sars). # 



(b) Barentsia gracilis and Pedicellina [Arthropodaria) benedeni. 



Comparison of the stem internodes of the multi-jointed forms of these species show 

 that their structures are identical in essential character. And yet from the characters 

 of the internodes Ehlers has distinguished between the genera Gonypodaria and 

 Arthropodaria, the former being " Zoarium stolonum filiformium internodiis alternis 

 prolatum phalangariis merosarcinis calyces gerens," the latter being defined as " Zoarium 

 stolonum filiformium internodiis alternis prolatum, phalangariis articulatis holosarcinis 

 calyces gerens." The " merosarcin " internodes are defined thus: " Bei ihr ist die 

 Phalange aus einer basalen dickeren, muskulosen und nachgiebigeren, und einer stets 

 muskelfreien, derbwandigeren diinneren Strecke zusammengesetzt ; solche Phalangen 

 nenne ich wegen der Beschrankung der muskulatur merosarcin" ; while "holosarcin" 

 internodes differ in consisting of " der aufrechten Strecke eines mehraxigen Basalgliedes, 

 welche in ihrer ganzen Lange gleichformig ist, und zwar dadurch, dass eine wandstandige 

 Muskelschicht unter einen weicheren, meist ringformig geriinzelten Cuticula liegt."f 

 Yet Ehlers makes reservations on behalf of Arthropodaria : " Urnatella und Arthro- 

 podaria nehmen eine Zwischenstellung ein [between the completely holosarcin and 

 completely mesosarcin groups], insofern der Muskelmantel in den gleichmassig dicken 

 Stengelgliedern nicht deren ganze Lange erfiillt." | And again : " Die Glieder der 

 mehrgliedern Trager sind bei Arthropodaria benedeni zwar gleichmassig dick, lassen 

 im ubrigen aber eine muskulose und eine muskelfreie Strecke unterschieden, von 

 welcher die letztere durch festere Chitinisirung der Wand die erstere ubertrifft. . . . Ich 

 bezeichne diese Glieder, wiewohl es nicht ganz zutreffend ist, noch als holosarcin. 

 Phalangarien mit merosarcinen Gliedern besitzt die Gattung Gonypodaria." § 



These reservations, it seems to me, almost nullify the distinctions between 

 Arthropodaria and Gonypodaria. So far as the type species of these two genera are 

 concerned, Gonypodaria nodosa (equivalent to the jointed specimens of Barentsia 

 gracilis) and Arthropodaria benedeni, the essential generic distinctions of Ehlers do 

 not exist, for in each case the muscle-strands are confined to the thin-walled expansions 

 of the stem, and only connective tissue passes from internode to internode, as in the 

 Hull specimens described above. It is evident that there is a greater perfection of 

 finish in the internodes of Arthropodaria benedeni, for they are more constant in dimen- 

 sions, and their chitinous cuticle and nodes are more strongly developed ; but " il s'agit 

 uniquement de l'exageration d'une particularite existant chez Pedicellina belgica " 

 (Foettinger, op. cit., p. 301), and can scarcely be regarded as of more than specific im- 

 portance. And if, indeed, it is not sufficient for the suppression of Arthropodaria that 

 its generic characters are essentially identical with those of Gonypodaria, then the fact 



* The mistake of ascribing Pedicellina belgica to P. cernua, in Jelly's Synonymic Cat. of Recent Marine Bryozoa, 

 London, 1889, p. 202, is obvious. 



t Ehlers, op. cit., p. 43. + Ibid., p. 146. § Ibid., p. 44. 



TRANS. ROY. SOC. EDIN., VOL. XLVII. PART IV. (NO. 27). 123 



