12 Proceedings of the Royal Physical Society. 
II.—Note on the Occurrence of Two Generations of the Nudi- 
branchiate Mollusca Lamellidoris bilamellata (Linn.) and of 
Archidoris tuberculata (Cuvier) in the course of a year. By 
L. P. W. Renouf, B.A., the Bute Laboratory and Museum, Rothesay. 
(MS. received 15th December 1915. Read 20th December 1915.) 
SYSTEMATIC observations, extending from February to October 1915, on the 
fauna of a short stretch of shore on the eastern side of the Isle of Bute, have 
discovered Lamellidoris bilamellata (Linn.) and Archidoris tuberculata (Cuvier) 
to be two of the commonest forms of nudibranchs in that region. Of these 
billamellata far outnumbers tuberculata, but the latter has a wider distri- 
bution. 
L. bilamellata was observed from 11th February 1915, when the observations 
began, until 28th April, and again from 27th July ; A. tuberculata was seen 
from 2nd March until 4th April, and again from 27th July. The latter was 
found in abundance also on 3rd May about half a mile from the former 
locality. 
LL. bilamellata was in abundance and spawning freely from 2nd March to 
29th March, after which date it decreased in numbers until 28th April. 
Between this date and 28th June it was unrepresented by either spawn or 
individuals. Absence from Bute made it impossible to make observations 
between 28th June and 27th July, but by this latter date bilamellata was 
again present in abundance, many individuals being in pairs, whilst a few 
were spawning. On 8th August, 10th September, and 11th October very 
large numbers were observed, a large proportion of them spawning. On 
9th August this species was seen in abundance on the lower piles of 
Rothesay Pier, some two miles from the former locality, both in pairs 
and spawning. 
A, tuberculata was seen in abundance from 10th March to 29th March. 
No spawn was seen on the former occasion but pairs were common, whilst on 
15th and 29th March both pairs and spawn were abundant. On 28th April 
only a few small individuals and a single coil of spawn were seen, but on 
28th May many large individuals and abundant spawn were found about half 
a mile from the former locality. 
On 25th June this species was quite unrepresented, but on each of 
the dates 27th July, 16th August, and 10th September a few small 
individuals were seen, and on 11th October one was found in the act of 
spawning. 
All the winter specimens of Z. bilamellata and their spawn-spirals were 
