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The tenth species of the genus Xanthidium, and the second ot the 

 Tubifera, is Tubiferum complex ; which differs from the last in this, 

 that the tubiform tentacula have branching terminations 

 or processes, but which are not uniform in their struc- 

 ture. Sometimes the orifice is separated into unequal 

 divisions of four, five, or six parts, thus (see figure) ; in 

 others like one variety of X. ramosum before noticed, the branching 

 terminations being of a more complex structure, thus ; 

 each branch having at its extremes a further ramifica- 

 tion, and which last, I am strongly inclined to consi- 

 der not a variety of the species, but the same as the 

 former in a more advanced state of development. I have arrived at 

 this conclusion after repeated observation and comparison of many 

 individuals of X. Tubiferum complex in my collection : and I think I 

 can clearly trace among them the gradual progress of the tentacula, 

 from the first separation of their orifices until they assume that form 

 which I deem the perfect type of the species. The following deline- 

 ations, sketched from the tentacula of two or three individuals in my 

 collection, illustrate my observation ; from these instances I further 



conclude that the terminations of the tentacula, in the same indivi- 

 dual, do not uniformly progress towards perfect form, but that some 

 of the tentacula attain to perfect development before others. The 

 first of these forms I consider the perfect characteristic of the species. 

 The tentacula apparent are from fifteen to eighteen ; the average dia- 

 meter is from -j-^y to -j-^-s- of an inch. This is the most common of all 

 the Tubifera, but all the Tubifera are rare compared with the other 

 eight species. 



The eleventh and last species of the genus Xanthidium, and the 

 third of the Tubifera, I have named Tubiferum recurvatum or pal- 

 maforme, the curved or palm-formed Tubiferum ; it differs from the 

 two preceding in having the tentacula decorated at their terminations 

 with a cluster of smaller curved processes, diverging from the orifice 

 of each tentaculum, and inclining back in the form of a cluster of 

 palm-leaves, from four to six in number. Next to Tubiferum simplex 

 this is the most rare of all the species : the average of their diameter, 



