322 PHYSALIA. 



by Liiine, on the ground that "Unquestionably the type of the genus and descrip- 

 tion was the first species." But Poche ( : 07), who has reviewed the early history 

 of Holothuria in detail, and whose conclusions are in accord with the Inter- 

 national code of nomenclature, has shown that this conclusion is not justified. 

 He points out that inasmuch as "Linne einem typus naturlich nicht bestimmt 

 hat, so mussen wir zur Festlegung desselben das Eliminations — verfahren aus- 

 venden." He has shown that the use of this method of choosing the type abso- 

 lutely precludes the selection of physalis, since this species was removed from 

 Holothuria to Physophora by Modeer in 1789, while two of the species enumer- 

 ated in the former genus by Linne in the 10th edition of the Systema Naturae 

 were still allowed to remain in it. Under the International code it is one of the 

 latter which must be selected as its type. The choice of Linne's Holothuria 

 'physalis for the type of Lamarck's genus Physalia, is then valid, and the further 

 fate of the genus Holothuria need not concern us. The relationship between 

 Physalia and Holothuria is the same as that between Porpita and Medusa (p. 

 329). In both the same conclusions are reached as to the validity of the 

 Siphonophore genera in question, a result fortunate for the sake of stability. 



PHYSALIA Lamarck, 1801. 



The collections of Physalia which I have examined, from the Atlantic, Pacific, 

 and Indian Oceans, entirely support Chun's ('97b) view that there are two 

 species, and two only, an Atlantic and an Indo-Pacific, the former chiefly char- 

 acterized by the presence of many, the latter of only a single "Haupttentakel." 

 Schneider ('98), believes that the two are merely varieties of one species. But 

 the fact that among the considerable number of specimens of the Pacific 

 species which have now been studied, not only by the early authors, but 

 recently by Chun ('97b), Agassiz and Mayer (:02), Lens and Van Riemsdijk 

 ( : 08) and by myself, none have more than one main tentacle, is good evidence 

 that this condition is the final one in this form. 



The fact that in its adult state the Pacific species resembles an immature 

 stage of the Atlantic Physalia has led to much confusion in the early literature 

 of the subject. 



Justification of the choice of utriculus as the specific name for the Indo- 

 Pacific species is given by Chun ('97b, p. 86), to whom I refer the reader for a 

 more extended review of the subject. I have not been able to consult the original 

 description myself. The Atlantic species is P. physalis Linne. Many authors 

 have used the earlier name arethusa Browne (1756), but this is pre-Linnean. 



