Though the number of new or supposed new species is so great, the number of new genera is comparatively small, not amounting to more than four. It has, however, been found necessary considerably to modify the characters of several other established genera, so as to include new species.
With respect to the geographical distribution of the species, my means of comparison have been pretty extensive. They have been derived from the examination of Mr. Darwin's and Dr. Hooker's collections, placed at my disposal by the kind liberality of Mr. Darwin--a considerable collection of South African species mainly procured from Mr. Bowerbank--and from the Collection of British and exotic Zoophytes in the British Museum, for the freest opportunities of examining which I have to thank Mr. Gray. From these various sources, and others of less account, I have been able to examine species from a very considerable extent of the earth's surface--more especially in the Southern hemisphere, and to arrive perhaps at as fair a view of the geographical distribution of species as the present imperfect state of Zoophytology will allow.
POLYZOA.
The number of species of Polyzoa is about fifty-four--belonging to twenty-four genera. Of these genera it is believed that four will be found to be new, or hitherto undescribed, and it has been deemed requisite to modify the characters of several others upon the more extended survey of species afforded mainly by the present collection. The new genera here instituted are:
Calpidium.
Diachoris.
Didymia.
Dimetopia.
And the genera whose characters it has been found requisite to modify are:
Catenicella.
Salicornaria.
Cellularia.
Scrupocellaria.
Bicellaria.
Canda.
Emma.
Acamarchis.
Caberea.
Of the twenty-four genera, three, or perhaps four, appear to be peculiar to the Australian seas. These are:
Calpidium.
Canda ?
Didymia.
Dimetopia.