Description of the Arguhis Caiostomi. 299 



spine. This joint is hollow and contains a retractile spine of a 

 brown color, capable of being projected into the terminating spine 

 of the joint. From the middle of the posterior surface arises a 

 jointed transparent process directed outward, extending beyond 

 the main branch of the antennae 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 antennae 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 antennae 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 antennas may be observed near the base of 

 the sucker. 



The organs of mandiicaiion 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 antennae. 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 aha', (Fig. 4.) At J is a 

 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 

 of the membrane that covers the anterior portion of the oval mass. 

 This anterior membrane is connected laterally with a slender bone 



