314 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



value of the numerical differences between pensile and macrodactylum 

 which appear from the present tables. 



x About 6 between 2 tentacles. 



2 About 8 between 2 tentacles. 



The last specimen is the type of Polycanna pwpurostoma Agassiz 

 and Mayer, which has papillae. 



I have not included Chun's (1896) specimen from Zanzibar be- 

 cause of lack of information as to excretory papillae and of the forms 

 of the tentacular bulbs. It had 84 canals and 10 tentacles — that 

 is, 8.4-1. 



The table shows a variation in proportional numbers of canals and 

 tentacles of from 1-1 to 6-1. Thus there are invariably considerably 

 more tentacles in proportion to canals than there are in pensile. 

 Another minor feature helping to separate the two is the fact that 

 anastomosis of the canals seldom or never occurs in macrodactylum, 

 while it is usually more or less evident in large specimens of pensile 

 (p. 312). 



In the specimens from the Philippines the bases of the tentacles 

 usually clasp the exumbrella more or less (pi. 43, fig. 7), but the pre- 

 cise conformation varies as noted above. 



The records for macrodactylum as here defined are chiefly from 

 the Indo-Pacific, where it is widely distributed in warm regions. I 

 have examined a typical specimen from the Gulf Stream. 



Genus ZYGOCANNA Haeckel, 1879. 



Zygocanna Haeckel -f- Zygocannota Haeckel + Zygocannula Haeckel. 



Mayer (1910) has summarized our vague knowledge of this, up 

 till now, problematical genus. Its distinguishing feature among 



