Description of the Argulus Catostomi. 299 
spine. This joint is hollow and contains a retractile spine of a 
brown color, capable of being projected into the terminating spine 
f the joint. . From the middle of the posterior surface arises a 
jointed transparent process directed outward, extending beyond 
the main branch of the antenne and terminated by three or four ter- 
minal transparent spines. ‘This process is also furnished with a spine 
near its extremity.—The posterior pair of the antenne is one third 
longer than the anterior, to which they are at base closely approxi- 
mate. They are four-jointed, slender and diaphanous. The basal 
joint is large and sub-cylindrical, with a few minute spines on its 
posterior basal portion ; second joint one third the diameter of the 
first, with a few spines at its apex. Similar spines are observed on 
the apex of the first, which is one half the length of the preceding. 
Apical joint half the penultimate in length and diameter, terminated 
by three or four transparent spines. From the base of the first pair 
of antenne arises a short, fleshy cone, directed backwards and down- 
wards, having at its apex a stout, corneous tooth. The insertion of 
the muscles moving the antenne may be observed near the base of 
the sucker. 
The organs of manducation are complex. The anterior organ is 
a sucker, inserted in a three-sided membranous transparent retrac- 
tile sheath, having free motion in any direction from its insertion in 
the fleshy parts below. While at rest it is directed forward and ex- 
tends to the base of the antenne. When the sucker is retracted 
within the sheath, a long ligulate muscle is observed lying loosely 
on the right, extending from the upper part of the sucker to the 
parts below its base. 
Below the insertion of the sucker arises a convex oval mass (Figs. 
.1 and 4,) containing the rest of the mouth apparatus. It has a mo- 
tion to some extent in every direction. Its lower half is covered by 
a lip, or thin transparent veil, capable of a backward movement; 
its upper limits are marked by the line aba’, (Fig. 4.) At bisa 
conical fleshy protuberance, inserted on the interior surface of the 
lip, and extending a little beyond its upper limits. Anterior to this 
lip lies transversely a bony arch (cc’,) of a brownish yellow color, 
curved forward and giving off obliquely downward on each side two 
bones, connected by a membrane. The extremities of this arch 
are gradually lost in the parts above. This arch is the lower limit 
the membrane that covers the anterior portion of the oval mass. 
This anterior membrane is connected laterally with a slender bone 
