134 LIVERPOOL BIOLOGICAL SOCIETY. 
dorsal ridges and epipodial processes, between Goniodoris 
and Ancula.t The anterior part of the body in the 
region of the rhinophore shows in transverse section 
(Pl. VI. fig. 7, e.p.) a prominent lateral ridge which becomes 
considerably lower as it is traced back (Pl. VI. fig. 8, 
right side), and then rises again at the sides of the bran- 
chie (Pl. VI. fig. 8, left side, and fig. 9) and immediately 
behind them to form prominent cerata comparable with 
those of Ancula (Pl. VI. fig. 10). These posteriorly placed 
cerata of Polycera contain numerous large glands (Pl. VII. 
figs. 3 and 4) which we shall have to refer to again in 
connection with Ancula (p. 136). 
Ancula cristata, Alder. 
This species was found by Dr. Hanitsch at Port Erin, 
in April, 1890, and we took it in extraordinary profusion 
at Hilbre Island in March, 1890. On one reef of rocks 
especially, a little way above low water mark, there must 
have been many thousands of specimens present. For 
yards 1t was impossible to walk without treading on them 
and handfuls were readily collected by scraping the speci- 
mens together from the mud-covered rocks. Many of these 
were kept alive and used for the experiments with fishes at 
the Aquarium described below. 
The variation in size and colouring of this species at 
Hilbre is very great, and the larger specimens are almost 
invariably white, light grey or almost colourless, while the 
smaller ones are more or less conspicuously ornamented 
with bright yellow. This species is very slimy, and a num- 
ber of specimens put together in a bottle very soon form a 
+ Garstang (loc. cit. p. 181) has already pointed out that the cerata of an 
allied form, Idalia aspersa, are plainly homologous with the ridges of 
Goniodoris &c., and the epipodial folds of Doris; and has expressed his 
belief that their homologues are to be found in Tritoniu, Lomanotus and 
Holis, See also, Herdman, Quart. Journ. Mier. Sci., vol. xxxix p. 42. 
