108 G. HERBERT FOWLER. 
had produced a certain deformation of the coral, which was 
recognisable from the exterior, and which probably consisted 
merely of an exaggerated growth of the septa at that point. 
In no other Bathyactis individual, either from the same or 
from other localities, could I find traces of further specimens 
of the Crustacean. Judged by the contents and appearance 
of the alimentary canal of Petrarca, it seems probable that its 
relation to its host is not a case of true parasitism, but that it 
sucks in the nutritive fluid produced by the digestion and 
maceration of the food of Bathyactis, and does not derive 
sustenance directly from the tissues of the polyps. It is in 
fact a case of commensalism in the sense defined by De Bary 
(‘Tagebl. Vers. Deutscher Naturforsch. u. Aertzte,’ 1878, 
p. 121) [see note, p. 119]. 
On an external view (figs. 1, 2) the animal is seen to be 
nearly spherical, measuring 1°5—1:‘8 mm. in diameter. The 
general relations of the body, limbs, and carapace are those of 
a Lepas without a peduncle, with the terminal penis bent 
forwards under the thorax, the limbs much reduced, the 
mantle not carrying calcareous plates, but greatly swollen by 
the growth of the internal organs into its substance. The 
carapace thus formed is a dorsal and lateral outgrowth from 
the anterior part of the thorax (not merely from the neck as in 
Lepas), leaving free the head end and the posterior part of the 
body. Between the two halves of the carapace are seen, in an 
external and ventral view (fig. 1), the head, some of the appen- 
dages, and the penis. The ventral part of the carapace is 
spinose, the dorsal smooth. 
On removing the carapace from one side the appendages 
come into view (fig. 3). A pair of pre-oral appendages or 
antenne extend forwards in fig. 1, both of which were visible 
in the specimen drawn in fig. 3 (the remaining appendages in 
this figure are those of the left side only). They are termi- 
nated by two strong dorsally-directed hooks, one of which, 
the strongest, is articulated to the limb; between these pro- 
jects on the ventral side a delicate-jointed spine (fig. 6). 
Besides these terminal joints the limb is divided into three 
