300 Description of the Argulus Catostomt. 
de, d’e’, which near the center of the sides of the oval mass (at e) 
curving suddenly inward and downward and at the same time enlarg- 
ing tends to the base of the maxilla. This bone at its angle e forms 
an ear-like projection to the oval mass. On each side of the center 
arises a curved, corneous and slightly colored maxilla (f, f’, Figs. 
4 and 5,) which extends forward beneath and beyond the arch; the 
broad inner edge of each is serrated. An indistinct line near the apex 
appears to separate a short apical joint. These maxilla approach 
at their extremities and are each connected at their base with one 
of the forks of a long, narrow, furcated bone g, which extends out- 
ward and as far forward as the attachment of the sucker sheath to 
the body, where it appears to be loosely connected with the sur- 
rounding muscles. The other fork of this bone is connected with 
the lateral bones before described as tending towards the base of the 
maxille after forming an ear-like projection. Between and con- 
nected with the maxille near their base, are two horizontal united 
processes, (h, Fig. 5,) which become visible on the retraction of the 
ip. 
The maxille are capable of a slight motion back and forth in con- 
nection with the ear-like projections, which is effected by means of 
muscles extended nearly in the direction of the bones just described, 
and inserted near the anterior part of the base of the suction feet. 
Between the two maxille laterally, the bony arch above, and the 
lip below, appears the orifice of the mouth, (above 6, Fig. 4.) Be- 
yond the maxille is frequently observed an internal longitudinal 
fissure, the opening of which is always accompanied with a retraction 
of the lower Jip. On withdrawing this lip, and forcibly severing 
and uplifting the bony arch with the membranes, and the maxille 
with the long narrow bones to which they are attached, a second set 
of organs, similar to the first, presents itself. The maxille of the 
inner mouth, which may, for distinction, be called the inner macilla, 
are in shape, situation and structure, like the outer. They are dimly 
seen from without, just in front of the external maxille, (Fig. 4-) 
The longitudinal fissure above described appears to be situated in the 
upper membranes connected with the inner mouth, and extends for- 
ward from the bony arch of the inner mouth between the maxille. 
In endeavoring to trace analogies between this mouth apparatus and 
that of the more highly organized Crustacea, we are led to believe 
that the sheath of the sucker represents the Jabium, which may be 
supposed to be greatly elongated, and by the union of its lateral 
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