1446 THE VOYAGE OF H.M.S. CHALLENGER. 



In fig. a.i.C, from another specimen, the flagellum is longer and contains twenty 

 distinct joints, of which the first is the longest. 



The Mouth Organs show no special characters of distinction from those of Primno 

 guerini; in the specimen figured the mandibles have a small one-jointed palp; in the 

 second specimen the mandibular palp was two-jointed, the second joint shorter than the 

 first. The condition of the antennae, as well as the fact that the mandibular palp had 

 not attained its full number of three joints, indicates that each of the specimens is a 

 male not fully adult. 



The Gnathopods show no difference from those of the preceding species, except 

 slight variations in proportion of parts, such as might belong to the individual rather 

 than the species ; it may, however, be noticed that the side-plate of the second 

 gnathopod is produced into an extremely sharp point, and the first joint less conspicu- 

 ously dilated than in the species compared. 



First Perseopods. — The side-plate is less produced in front ; the indents of the 

 third and fourth joints are more pronounced, and the fourth joint is as long as the fifth. 



Second Perseopods. — The fourth joint is longer than the fifth. 



Third Perseopods. — The teeth on the front margin of the wrist are as follows, a 

 moderately long one with a denticle on its upper margin, two short, a long, four short, 

 a very long one, two short, a long, and three short, close to the hinge of the fifth joint ; 

 the fifth and sixth joints together are not as long as the fourth, and the sixth joint or 

 finger is not half the length of the fifth joint. The teeth of the margin of the fourth 

 joint seem much inclined to vary, depriving them of their value as specific characters ; 

 thus in the second specimen in one limb these teeth were as follows — one long, two short, 

 one long, four short, one long, three short, one long, three short, the last of these three 

 being double-tipped ; in the other limb they were one long, two short, one long, three 

 short, one broken (probably long), three short, one long, four short, the last double -tipped. 

 In the female specimen the teeth on one limb were — one moderately long, two short, 

 one long, four short, one long, four short, one long, four short, the last double-tipped ; 

 on the other limb they were — one long, three short, one long, four short, one long, 

 three short, one long, five short, the last double-tipped. 



Fifth Perseopods. — These seem to show the most characteristic differences ; the first 

 joint is a good deal narrower distally, having a very convex, slightly serrate, hind margin, 

 and a sinuous front margin which is concave above ; the five following joints together 

 considerably shorter than the first joint, the first four with shape and proportions nearly 

 as in Primno macropa ; the finger half the length of the preceding joint or less, with 

 the front margin nearly straight to the apex, then oblique for a very short distance, 

 that portion pectinate with some microscopic hairs or spinules, the terminal one being 

 the strongest, projecting from the tip of the hind margin which as in the other species 

 is bent sharply round at its apex. 



