AMERICAN PARASITIC COPEPODA. 249 
identical ; a conclusion which is rendered more probable by the fact 
that the hosts both belong to the subgeneric group of the Charrs. 
ACHTHERES MICROPTERI, 7. 8. 
The specimens for which I have selected the above specific name 
were found in considerable numbers, both male and female, in the 
mouth cavity and on the gill-arches of the small-mouthed Black Bass 
Micropterus salmoides {(Lac.) Gill]. As far as the size of the female 
is concerned, and the character of its fixation in the mucous mem- 
brane of its host, it might well be referred to A. percarum V. Nord. ; 
but the relatively larger size of the male, the constant downward 
direction of the arms, the shape of the bulla, some details of structure 
in the other appendages, and the cylindrical form of the egg-sacs, 
point to the specific distinctness of this form. I am assured by 
Prof. D. 8. Kellicott that it is also distinct from his A. Ambloplytis 
from the mouth of the Rock Bass; otherwise I should have been 
inclined to suspect the identity of the two American forms. I have 
never met with any Achtheres in our common Perch. 
The female measures on an average 4 to 44 mm., the cylindrical egg- 
sacs 24 mm. Fig. 1 represents the appendages of the head from the 
ventral aspect. The antennule are attached at some considerable 
distance behind the mouth: their basal joints are the longest and 
stoutest of the three. The internal rami of the antenne seem to 
present little difference from A. percarum, but the ends of the 
external rami are furnished with toothed sickle-shaped spines. 
The mandibles, Fig. 2, have 9 teeth, of which the third is the 
shortest of the first six, and the last three are successively smaller. 
The inner edges of the mandibles are sharpened into a knife-edge, 
which is broadest immediately behind the teeth. 
The maxille are two-jointed—the distal joint bearing a lateral 
two-jointed bristle-like palp, and two terminal rami of the same 
character. The maxillary sternum forms a prominent fold (muzs., 
Fig. 1), owing to the advance of its appendages in front of the 
attachment of the antennz. 
The internal maxillipedes are three-jointed: the basal joints are 
united, the second are stout and furnished with a hook on the inner 
side (vide left side of Fig. 4), while the third are armed with a 
strong terminal curved claw articulated to the joint, which on its 
inner aspect is further furnished with two trenchant serrated ridges, 
