16 THE HYDROIDS. 



Versluys' s statement is, "Ainsi, sur une coupe transversale d'un tronc prin- 

 cipal assez pres de son sommet, je corapte trente oa trente-et-un tubes 

 peripheriques, entourant le tube axial d'une couche triple." The size of the 

 pinnules and the number and arrangement of their peripheral tubules is like 

 that given by Versluys. 



In the short uncovered, distal portions of the axial tube the hydrothecae 

 are attached to the stem in their basal part for nearly half their entire 

 length. After a brief soaking in caustic potash they are partly separated 

 (PI. 11, fig. 3), while after boiling in caustic potash they become entirely 

 free (PI. 11, fig. 4 ; PI. 12). Pictet and Bedot have already called attention 

 to this fact. It is also to be noted that after this treatment the hydro- 

 thecae of the main stem appear somewhat pedunculated, while those of the 

 pinnae do not (PI. 12; PI. 13, fig. 1). . 



The two localities for this species are off the Galapagos Islands in the 

 Pacific, and off the Testigos Islands some fifty miles north of Venezuela in 

 the Caribbean Sea. This is another of those interesting cases where the 

 same marine form is found on both the Atlantic and Pacific sides of the 

 Isthmus of Panama to which Mr. Alexander A<>-assiz first called attention in 

 1888. 



Kirkpatrick in 1890 wrote, "It would appear, then, that Perisiphonia is 

 synonymous with Zygophylax." I agree with him, and with Jaderholm, 

 that the slight difference of the continuation of the peripheral tubes quite or 

 not quite to the distal ends of the stem and branches is not a sufficient basis 

 for generic distinction, and therefore the species described as Perisiphonia 

 must be classified as of the genus Zygophylax. This genus now comprises 

 those seven species: — 



Zygophylax profunda Quelch, 1885, Cape Verde Islands 500 fathoms 



Zygophylax (Perisiphonia) pectinata Allman, 1888, New Zealand 700 " 



Zygophylax (Perisiphonia) pectinata Pictet and Bedot 1900, Gulf of Gascogny 300 metres 



Zygophylax (Perisiphonia) pectinata Pictet and Bedot, 1900, Azores . . . 318 " 

 Zygophylax pectinata, Jaderholm, 1903, Eastern Atlantic (about 500 miles 



■west of Gibraltar) 102 fathoms 



Zygophylax opereulata Jaderholm, 1903, Patagonia, Cape Valentyu .... 150 " 



Zygophylax (Perisiphonia) filicula Allman, 1888, Azores 450 " 



Zygophylax (Perisiphonia) filicula Allman, 1888, Australia 150 " 



Zygophylax tizardensis Kirkpatrick, 1S90, China Sea 35 " 



Zygophylax chazaliei Versluys, 1899, Testigos Island 80 metres 



Zygophylax chazaliei Clarke, 1907, Hood Island 300 fathoms 



Zygophylax biarmata Billard, 1905, Bay of Biscay not given 



