368 MR. HANCOCK ON THE ANATOMY OF THE FRESHWATER 
Amongst the known species was a fragment of Alcyonella, most 
probably A. stagnorum ; but its characters could not be deter- 
mined on account of the imperfection of the specimen. rederi- 
cella sultana occurred abundantly, and of very luxuriant growth, 
spreading over the under surface of stones in patches of three or 
four inches’ extent. Of the new species, two belong to Plumatella 
and one to Paludicella, a rare genus, of which there was but one 
species previously known, and that, I believe, had been found only 
in Ireland, and in two or three localities on the continent. 
The anatomy of the freshwater Bryozoa had been very little 
studied, on this side of the Channel, before Professor Allman took 
up the subject, and he has handled it so well that little is left to 
be done. Indeed so complete are the results of this naturalist, 
that, perhaps, the publication of my own may appear almost un- 
necessary. My investigations, however, carried on, as they have 
been, perfectly independent of the researches of others, may not 
be without some value even where novelty is wanting. Micro- 
scopic investigations conducted by the aid of transmitted light 
are liable to error. Frequent examinations in such cases are 
therefore necessary, and observations independently prosecuted 
are of peculiar value. Consequently, I do not hesitate to give 
the result of my own labours on this subject, fraught as it is with 
difficulty, not fearing to mislead in a path already so well trodden. 
Of the anatomy of these animals I shall have to confine my- 
self almost entirely to that of Plumatella, Fredericella and Palu- 
dicella. Of Alcyonella I can say but little, having seen only an 
imperfect specimen, and none of the other freshwater forms have 
come under my notice, 
Plumatella and Fredericella resemble each other very closely 
in their anatomical structure, notwithstanding the external 
difference of their polypes. Paludicella, however, shows some 
very interesting modifications, particularly in the muscular sys- 
tem: but before entering on the internal anatomy, it will be 
necessary to examine the characters of the polypidom, and to 
trace its relationship to the polype. 
The polypidom of Plumatella Allmani, Pl. VI, figs. 3, 4 and 
5, and of Fredericella sultana is tubular, branched and carinated 
