244 AMERICAN PARASITIC COPEPODA. 
pairs, without the 2 spines on 8rd joint. Furcal bristles 4,—2 prin- 
cipal, 2 subsidiary, of which one very short. 
THE APPENDAGES.—ANTENNUL. 
One of these is represented in Fig. 13, from the posterior 
aspect. 
They are 6 jointed, and originate on the under side of the head at 
some little distance from each other. There is no antennulary 
sternum. Of the joints the 2nd is the largest, and with its 
exception, the 6th the longest. All the joints bear simple bristles, 
the longest of which are nearly as long as the antennule itself. The 
bristles of the first four joints are chiefly directed downwards ; of 
the two terminal joints backwards and outwards. Into each bristle 
branches of the antennulary nerve may be seen to pass. 
ANTENN&. 
As in the other species of the genus, the antenne form strong 
prehensile claws by which the animal clings on to the gill-filaments 
of its host. The antennary sternum is well developed (Figs. 12 and 
14, st.), and enters at its extremities into the construction of the 
hinge-joints, which the antenne form with their sockets. The basal 
joint is much inflated (as in #. gibbus V. Nordmann) on its outer 
and lower aspect, while on the opposite it is strengthened by 2 
chitinous ledges, which descend from the hinge between it and the 
succeeding joint (c’, Fig. 14) to the socket (c'). When viewed 
from the surface one of these ledges gives the appearance of a 
diagonal division in the basal joint.'. The hinge between the 2nd 
and third joints is somewhat complicated, but its arrangement, as 
well as those of the chief flexor and extensor muscles entering the 
appendage, may be studied in Fig. 14. The terminal joint is 
particularly short and curved; in this respect unlike the same part 
in E. Sieboldii.? 
APPENDAGES OF THE MOUTH. 
These have been only satisfactorily described for LZ. Sieboldit by 
Claus. 
1 Vide Olsson, Ofversigt af Kong]. Vet. Akad. Forhand, 1877, No. 5, p. 76. 
2y. Claus Zeit. Wiss. Zcol., Tal. XXIIL., Fig. 14. In a revision of the species of 
Ergasilus, it will probably be found that apart from the size, form of body, and length of egg- 
sacs, the form of the appendages will afford valuable specific characters. As far as I am 
aware, however, Claus’ figures are the only ones which possess the- necessary accuracy of 
detail. 
