REPORT ON THE SIPHONOPHOR^. 351 



forms, which connect the different " good species " of this transformistic group, partly 

 to the great confusion of the voluminous literature on this subject. Most authors have 

 founded their specific distinctions upon slight differences in the variable form of the very 

 contractile pneumatophore and insignificant varieties of colour. The accurate anatomical 

 examination of the siphosome, the composition of the cormidia, and the relations of the 

 different clustered medusomes has been much neglected, and requires a further more 

 critical comparison (compare Huxley, 9, p. 99, and Chun 83, p. 557). Judging from the 

 extended observations of numerous Physalige collected in different seas which I have 

 been able to compare recently, I think that the following four species of Physalia may 

 be distinguished provisionally: — (l) Physalia pelagica (South Atlantic); (2) Physalia 

 cornuta (Indian Ocean); (3) Physalia utriculus (Pacific); and (4) Physalia megalista 

 (Indian Ocean and South Atlantic). 



Physalia megalista, Lamk. (Peron, 14, pi. xxix. fig. 1), differs from the three other 

 species in the complete union of all the cormidia, as in Caravalla maxima; there is 

 wanting here the free interval which separates the small basal cormidium (on the distal 

 end of the trunk) from the main mass of clustered cormidia on the ventral side of the 

 pneumatophore. This interval between the two groups of cormidia (the smaller posterior 

 and the larger anterior), as well as the composition of these cormidia, is different in the 

 three other species of Physalia ; the structure, too, of the pneumatophore, the number 

 of chambers in its crest, and the mode of attachment of the appendages to the trunk, 

 seem to offer marks for a more accurate distinction of these species. (Compare the 

 figures of the Southern Atlantic Physalia pelagica by Eysenhardt, 77, p. 45, Tab. xxxv. 

 fig. 2 ; of the Indian Physalia cornuta by Tilesius, 76, p. 42 ; and of the Pacific Physalia 

 utriculus by Eschscholtz, 1, p. 163, Taf. xiv. figs. 2, 3 ; and in Cuvier's Regne Animal 

 Illustre, Zoophytes, pi. 58, fig. 4.) 



Genus 75b. Caravella, 1 Haeckel, 1888. 



Definition. — Physalidas with a polythalamous crest on the dorsal side of the large 

 vesicular pneumatophore. Siphosome with several large main tentacles of about equal 

 size. 



The genus Caravella comprises those Physalidse which agree in the possession of a 

 polythalamous crest on the dorsal side of the large pneumatophore with the preceding 

 true Physalia (s. restr.), but differ from them in the possession of numerous large main 

 tentacles, besides a great number of small accessory tentacles (or palpacles). Caravella 

 exhibits therefore the same relation to Physalia which the crestless Arethusa bears to 

 Aloplxota. The cormidia are in Caravella polygastric and loose ; the number of siphons 



1 Caravella, the old name of Physalia as usually employed by the Italian and Spanish sailors [Medusa caravella, 

 Linne). 



