NO. 2063. NORTH AMEltlVAN I'AltAiHTIC C0PEP0D8— WILSON. 661 



terior ends, but are separated ventrally by the enlarged genital 

 segment. 



First antennae short, slender, conical, the basal joint much 

 enlarged, the two terminal joints narrowed; second antennae 

 biramose and turned down squarely across the frontal margin, both 

 rami one-jointed, the endopod (dorsal) half as long again as the 

 exopod and bluntly rounded, the exopod with two short spines at 

 the tip and a short, one-jointed process on the ventral surface. The 

 mouth-tube is broadly conical and extends beyond the tips of the 

 second antennae. The first maxillae are short, stout, bipartite, and 

 destitute of a palp. The second maxillae are comparatively long 

 and wide. Each is flattened into a broad band of cartilaginous sub- 

 stance, manipulated by three longitudinal muscles. These bands 

 pass entirely around the gill filament, and thus hold the parasite 

 securely in place. The nature of these second maxillae has puzzled 

 all the observers who have thus far described any species of tliis 

 genus. Does each of the ribbonlike bands represent a separate 

 maxilla ? Or does the right half of both bands represent the right 

 maxilla and the left half the left maxilla ? If the former, does each 

 maxilla extend around the filament from its own side, or do they 

 both start from the same side? If the latter, how are the bands 

 joined where they meet? In adult specimens these maxillae are so 

 completely fastened that one can get no idea of the way in which 

 they are formed. 



Fortunately, one of the specimens obtained at Beaufort was a 

 young female in wliich the second maxillae were not yet fully devel- 

 oped, and this specimen (fig. 128) answers our questions for us. 

 Each band represents a separate maxilla, and the two are anterior 

 and posterior instead of right and left. Furthermore, both bands 

 started on the midline of the ventral surface of the cephalothorax 

 and extended around the filament from the left to the right side of 

 the parasite. Here on the right side and sunk into the surface of 

 the cephalothorax are two sockets, into which the blunt claws on 

 the tips of the maxillae fit. The claws and the sockets are gradually 

 fused together, until in the adult they can no longer be separated. 

 Each maxillae, therefore, corresponds to an ordinary maxilla flat- 

 tened laterally. As these maxillae migrated toward the ventral 

 midline the base of one moved a little forward and the base of the 

 other a little backward, so bringing the two into line. From the 

 arrangement of the claw on the tip of each maxilla it would seem 

 as if there was no orientation during this migration. After the 

 migration the maxillae extended around the filament, with the inner 

 surface of the left hand one and the outer surface of the right hand 

 one next to the filament. 



