been obliged to dépend upon published descriptions of this species, and at almost 

 ail points at which authors make spécifie différences between atlanticum and gigan- 

 teum I find, among the large number of spécimens at my disposai, agreements with 

 both,and complète gradations from one to the other; in the case of the zooids, often 

 within the same colony. Infact, I am compelled to question the actual existence of 

 both atlanticum and giganteum as distinct species. For example, Savigny, 1816, was 

 first to emphasize différence in form of the colony as being distinctive of the two 

 species, he stating the atlanticum colony to be conical, and that of giganteum 

 cylindrical. » « I find colonies that would certainly hâve to be described as cylin- 

 drical, and others that would as surely be regarded as conical. But there are 

 numerous others, again, that the narrowing toward the closed end is so exceedingly 

 graduai and slight that to say they are conical would be no more apt than describe 

 the trunk of one of our tallest silver fir trees as conical. Again, as to the structure 

 and arrangements of the test processes, I find, even in the same colony, essential 

 agreement with those said by Seeliger to be characteristic for P. atlanticum var. 

 tuberculosum ; and at the same time with those described and figured by various 

 writers for P. giganteum. Turning to the ascidiozoids, I hâve not had much better 

 luck than with the colony as a whole. Thus the branchial siphons are said by Seeli- 

 ger (« Schlundrohr » of this writer) to reach a much greater length in old zooids of 

 giganteum than they ever do in atlanticum. In the same colony I find old zooids with 

 long siphons, but others again, certainly equally old, as judged by position in the 

 colony and development of the gonads, with the siphons decidedly short and wide.» 

 « So far as concerns the branchial sac, the testes and the musculature, upon which 

 some reliance is placed by various writers for separating the two species, I am ofthe 

 opinion that individual variation is so great hère, that the value of différences can 

 be determined only by extensive quantitative studies, careful regard being had to 

 the âge of the zooids. The color variation is also great, this ranging from deep pink 

 to an entire absence ofthe color. » 



C'est avec intention que j'ai cité les conclusions détaillées de Ritter, car je ne 

 saurais exprimer mon opinion avec d'autres termes et je voudrais éviter des 

 répétitions. Pyrosoma giganteum Lesueur et P. atlanticum Péron sont les extrêmes 

 d'une espèce, ou l'une est la variété de l'autre. Suivant les règles de la priorité, le 

 nom de l'espèce devrait être atlanticum. Mais, parce que la forme giganteum est plus 

 fréquente que la forme ^//an/ïCMm, je propose de nommer l'espèce : P. giganteum, et 

 la variété atlanticum. Parmi ces deux formes il y a toutes les modifications possibles. 

 Souvent une colonie montre dans quelques ascidiozoïdes les caractères de giganteum 

 et dans d'autres ceux à'' atlanticum. Pour cette raison, je crois qu'il est inutile d'énu- 

 mérer toutes ces variétés. 



A Naples on nomme P. elegans une forme avec des appendices buccaux extrê- 

 mement grands. Ce nom doit être naturellement abandonné, de même que les noms 



