32 
Busk on Avicularia. 
Of angular imbedded avicularia, the numerous species 
of the genus Catenicella afford examples. This organ, in 
fact, in that genus, often furnishing very satisfactory specific 
characters. In some, as C. plagiostoma, it is of gigantic size, 
in others very minute, and in one it seems to be aborted, being 
replaced by channelled processes, C. carinata. In several 
other species it is in some cells replaced by long ascending 
cornua or hollow spines, as in C. cornuta and C. taurina. 
The genera Menipea, Cauda, ScrupoceUaria, and Cellularia, 
are respectively distinguished by the presence or absence of 
avicularian and vibracular processes. The former are always 
of the sessile kind, either immersed, and at the superior and 
outer angle of the cell, or projecting and placed on the front 
of the cell, below the level of the aperture. In the genus 
Menipea, there is an angular, superior, imbedded avicularium 
in many of the cells, and a projecting sessile organ on 
the front of the cell below the aperture, and no vibracula. 
The British species, Menipea ternata, affords an instance ; 
the other species similarly characterized, are — M. cirrata, 
M. fiiegensis, M. triseriata, M. ornata, M. patagonica, and 
M. multiseriata. The genus Cauda, differs from Scrupocel- 
laria, mainly in the want of any avicularian process at 
the superior and outer angle ; but the cells sometimes have a 
sessile avicularium in front, below the aperture. This is 
particularly the case with Cauda arachnoidea, in which the 
avicularia appear to occupy an unusual position : they do not 
seem to be seated on the fronts of the cells themselves, but to 
form a series afhxed to the median septum between the two 
rows of cells ; and, what is very curious with regard to them 
in this species, they are apparently developed long after the 
completion of the cells, seeing that they are totally wanting 
in the upper and younger portions of the branches of 
the polyzoary, and gradually increase in size towards the 
inferior portion. In Scrupocellaria, we arrive at the full 
development of these accessory organs ; the species in this 
genus being all distinguished by their being furnished with 
both avicularia and vibracula. Of the former, one is always 
imbedded in the superior and outer angle, as in Scrwpocellaria 
scrupea, S. scruposa, and S. Macandrei ; whilst in others, such 
as S. ferox, and S. cervicornis, there are superadded to these, 
sessile avicularia on the front of the cell below the aperture, 
in the former species, of colossal dimensions. The genus 
Cellularia, again, is distinguished by the entire absence 
of both avicularia and vibracula. The British form Cellularia 
Peachii, affords an instance. 
The genus Caberea, except in tlie single species above re- 
