I9T4- CoLGAN. — Opisthobranch faima of Co, Dubliji, 163 
in the north, Skerries Bay and its islands, have been well 
worked and have yielded respectively 28 and 32 Nudibranch 
species. 
So wide is the distribution of marine organisms in general 
that it would be idle to seek for any well marked local 
groups within the limits of the Dublin area. Though a few 
species arc apparently absent from one or other of the three 
localities which have been most fully examined, Skerries 
in the north, Malahide in the middle, and Dalkey Sound 
in the south, there can be little doubt that further explora- 
tion would show that all of the Opisthobranch species here 
recorded are distributed throughout the area. So no 
attempt has been made here to trace out local peculiarities 
of distribution. But the living organism has been studied 
so far as opportunity offered ; and in the following pages 
the usual details as to habitat and frequency have been 
supplemented by the results of personal observation and 
research on the bionomics, variation, embryology, and 
anatomy of a large mimber of species which the writer 
succeeded in maintaining alive for periods ranging from 
a few days up to ten weeks. 
The nomenclature of Nichols' List of the Marine Mollusca 
of Ireland, so well known to Irish students of the group, 
has been adopted here, and following the example of the 
List the specific name used .by Jeffreys in his British Con- 
chology has been added in italic type where it differs from 
the List name. Previously unpublished results of the 
writer's own dredgings and shore gatherings are distin- 
guished by the initials, N.C., and to obviate somewhat the 
vagueness inseparable from the use of such terms as " rare," 
" frequent," and " common " as indications of the standing 
of the various species, details are given of the number of 
specimens taken and of the number of dredgings in which 
the non-littoral species occurred. The maximum size 
attained by each species has been noted in most cases, the 
measurements being given uniformly in millimetres of 25 
to the inch. 
In the preparation of this account of the Dublin Opistho- 
branchs I have received valuable aid from Mr. A. R. Nichols 
A 2 
