Busk on Avicularia 
3a 
ferred to, and which might, perhaps, on that account, almost be 
regarded as the type of a separate genus, is distinguished, and 
very remarkably so, by the extraordinary isize and curious 
arrangement of the vibracula on the back of the branches, 
which thence derive a very close resemblance to an ear of barley. 
It is in this genus that the vibracular organ acquires its ex- 
treme development. A British example is afforded in Caherea 
Boryi, a not uncommon denizen of the Channel coasts. In 
the genus Emma, we have afforded an instance, in which the 
position of the organ may be used in the generic character. 
In the species belonging to this genus, the sessile, lateral 
avicularium is situated on a level below the aperture. E. g.^ 
Emma crystallina and E. tricellata. 
The peculiar disposition and form of the avicularia, in 
Notamia, have been sufficiently adverted to in this and my 
previous communication to the Society. 
It would require too much of your time and too much 
space to enter very particularly into all the instances in which 
I have found tlie form, position, and existence of avicularia 
and vibracular processes useful in the classification of species. 
The above remarks, hasty as they are, will serve to give 
an idea of the extent to which they may be so employed ; 
and I would only observe, in addition, that a similar atten- 
tion to these organs will be found indispensably requisite for 
the due appreciation of specific and even generic distinctions, 
in the difficult and hitherto much confused families of the 
FlustradrB, Membraniporidce, and especially of the Celleporidce, 
EscharadcB^ and Selenariadce. In Lepralia, particularly, in 
which genus I have placed nearly 60 species, I have found the 
use of these organs of the utmost importance, and easily avail- 
able. In fact without them it would have been a most difficult 
task to marshal into due order such an irregular and mutinous 
host. For the mode in which I have so employed this 
character, I must refer you to my ' Catalogue of Marine 
Polyzoa,' just published by the British Museum, and will 
conclude by saying, that the names of the Polyzoa here em- 
ployed are those by which they are distinguished in that 
work, in which the appropriate synonyms will be found. 
