PARASITIC COPEPODA. 199 



can be seen the powerful muscles which move those appendages; and which radiate 

 outward from the basal joint of the antennae to the lateral margin of the carapace. 



The dorsal surface has hut a single pair of grooves, one on either side separating 

 the lateral areas from the central cephalic area. Eyes moderately large, situated 

 close to the anterior margin and in contact with each other on the mid-line, but not 

 fused. In front of the eyes and on the very margin is a pair of elliptical spots, a 

 little larger than the eyes and raised above the surrounding surface like a pair 

 of lenses. These correspond exactly with the so-called " conspicilla " found by Dana 

 in his Specilligus curticaudis, and which occur also in the males of other species 

 belonging to the Pandarinse. They have also been noted by Kroyer in the male of 

 Trehius caudatus, but are not found in the male of the new species of Trebius just 

 described. In the present genus they are much farther forward and nearer together, 

 being just in front of the supra-cesophageal ganglion. 



The second, third, and fourth thorax segments are free and diminish regularly in 

 size. The second segment is the same width as the body of the carapace and its 

 lateral plates are as wide as the lateral lobes of the carapace. The third and fourth 

 segments are considerably narrowed, but even the fourth is more than twice as wide 

 as long, and the basal joints of the legs attached to both these segments closely 

 resemble in dorsal view the lateral lobes of the carapace and the lateral plates oil the 

 second segment. 



The genital segment is quadrangular, a little wider than long, and a little narrower 

 than the fourth segment. The processes at the posterior corners are very small, and 

 the fifth legs are almost invisible dorsally. The entire ventral surface of the genital 

 segment is covered with stout scattered spines which point diagonally backward. 

 These are thickest along the sides and must furnish a very effective preventative 

 against slipping, as in the genus Argulus. 



The abdomen is three-eighths the length of the genital segment, one-fourth wider 

 than long, aud one-jointed, with a shallow anal fissure. The anal laminae are 

 quadrangular-oblong, of medium size, each armed with four large plumose seta?. 

 Three of these are terminal, while the other comes out of the lateral margin near the 

 anterior end. 



Of the appendages, the anterior antennae are large and prominent, two-jointed, with 

 the joints about the same length, but the basal one considerably thickened. Each 

 antenna is one-fourth longer than the frontal plate from whence it comes. The setae 

 and spines are similar to those in the Caliginae. The second antennae are stout and 

 of the same pattern as in Caligus. The terminal claw fits into a small pocket made 

 for its reception in the ventral surface of the carapace near the margin (fig. 37). 



The first maxillae and furca are entirely lacking. The mandibles are slender, 

 three-jointed, and armed with hook-like teeth along the inner margin of the slightly 

 curved terminal joint. The mouth-tube is triangular, with a narrow and well-rounded 

 tip ; the mouth-opening is terminal and quadrilateral, with a heavy fringe of hairs. 



