40 MARINE POLYZOA. 



Colour white or yellowish ; forms close rounded tufts 2 to 3 

 inches high and wide, composed of uniform dichotomously divided 

 branches about |th of an inch wide, and which become wider 

 towards their truncate extremities. The vibracula are very large, 

 and though distinctly denned, are yet sufficiently transparent to 

 allow a view of the lozenge-shaped cells. The central rows of 

 cells vary in number from two to five, and the cells composing 

 them are arranged with extreme regularity. The marginal rows 

 are placed in a plane posterior to the central, and the cells of 

 which they are composed are widely different from the central. 



It is not easy to distinguish the narrower forms of this species 

 from Caberea hookeri, and they may not improbably really 

 belong to one and the same species, differing only in consequence 

 of the difference in the localities in which they are found. The 

 warmer latitudes of New Zealand and Australia may readily be 

 supposed to produce a more luxuriant growth, and consequently 

 wider and stronger branches of the polyzoary. But there are 

 other differences, which though less obvious, would better serve 

 to indicate a specific distinction between the two forms. In Cab. 

 hookeri there is a large tubular spine on each side of the mouth 

 in the lateral cells, and each of the central cells, or nearly so, are 

 furnished with an anterior avicularium, below the aperture and 

 to one side. The lateral avicularium also of the marginal cells 

 is much larger. 



2. AMASTIGIA ( priv., /xao-ri). 



An avicularium to about each three cells on the back of the 

 branches (no vibracula). 



In this genus the vibracula on the back of the branches are re- 

 placed by avicularia ; but it is to be remarked that in these avi- 

 cularia, contrary to what usually obtains in those organs, the 

 moveable mandible, when closed, points downwards ; in this re- 

 spect resembling the seta of the vibraculum, with which it is in 

 fact strictly homologous. 



1. AMASTIGIA NUDA. PL XXXVI. 



Cells bi-quadriserial; posterior avicularia small, the mandible 

 pointing downwards. A lateral and anterior avicularium to each 

 lateral cell : an anterior one to each of those in the central rows. 

 Aperture oval, with a broad pedunculate operculum and two 

 spines on each side above. 



Caberea nuda, Busk, MSS. t. 36. 

 Hab. Tierra del Fuego, Darwin. 



