‘ 
III PODOPLEA—ISOKERANDRIA 73 
completely segmented thorax, and lives clinging on to the female 
by its prehensile second antennae—Chondracanthus, Lernentoma. 
Fam. 7. Philichthyidae—These parasites, which are hardly 
known to occur in British waters,’ are mucus-feeders and infest 
the skin of Teleosts, e.g. the Sole; often taking up a position in 
the lateral line or in a slime canal. They show a similar sexual 
dimorphism to the foregoing family, the adult female being 
extraordinarily drawn out into finger-like processes (e.g. Philich- 
thys)* or else long, slender, and Nematode - like, with much 
reduced appendages (Lernaeascus), while the male retains a more 
normal structure. As in all the foregoing forms there is no siphon. 
We now return to two semi-parasitic families, Fam. 8, Nereico- 
lidae, and Fam. 9, Hersiliidae, in which there is certainly no 
well-developed siphon, but the upper and under lips protrude, 
forming a hollow between them in which the mouth-parts work. 
Both families are ectoparasites which frequently leave their 
hosts, and they retain their segmentation and powers of swim- 
ming. Perhaps the best-known form is the Hersiliid, Giardella 
callianassae, Which lives in the adult state in the galleries ex- 
cavated in the sand by Callianassa subterranea, gaining its 
nourishment as an ectoparasite on the Decapod. The larvae are 
pelagic, and are said by Thomson® to occur in Liverpool Bay. 
List* describes Gastrodelphys, a parasite of doubtful position, 
from the gills of tubicolous worms, such as Myzxicola and Sabella, 
which possesses a perfectly siphonostomatous mouth. 
The remaining families to be dealt with are those containing 
all the fish-parasites which possess a true siphonostome, as well 
as the siphonostomatous family Choniostomatidae, which is para- 
sitic on other Crustacea. In all these forms the mouth is pro- 
longed into a tube in which the styliform mandibles work. 
Fam. 10. Caligidae.—Ectoparasites on fish, lodging most 
frequently in the gill-chamber. In imost of the genera the 
segmentation and power of swimming are retained in both sexes, 
the sexual dimorphism not being very well marked, though the 
males are smaller than the females, and were in some cases 
originally described as belonging to a special genus Nogagus. 
-! The Cambridge Museum possesses two specimens of Philichthys Pee from 
the frontal bones of a Swordfish (Xiphias gladius) taken off Lowestoft in 1892. 
2 Claus, A7vb. Zool. Inst. Wien, vii., 1888, p. 281. 
3 Proc. Biol. Soc. Liverpool, i., 1887. 4 Zeitschr. wiss. Zool. xlix., 1890, p. 71. 
