486 



CRUSTACEA. 



above the base of the eyes, so that the tarsus hangs down in front. 

 The second and third pairs fold up and partially overlap the sides of 

 the carapax, beneath the fourth or penult pair, or, as is sometimes 

 seen, the third pair is thrown forward like the fourth. A species 

 very near Megalopa mutica, abundant near the Cape of Good Hope 

 (and referred to this species probably by Krauss, in his Sudafrik. 

 Crust., p. 54), is figured on Plate 31, with the legs in the position 

 they had while the animal was swimming. This position is not often 

 observed, since the animal, when disturbed, is almost sure to swim 

 with the legs extended; and the hinder legs are mostly like the 

 others in form and habit. On the same Plate, this position is shown 

 for another species from the Sooloo Sea ; in the former, the surface of 

 the carapax is simply a little depressed or concave for the folded pos- 

 terior legs (Genus Marestia), while in the latter (Genus Monolepis), 

 as shown in figure 5 b, there is an abrupt channel. 



The channel in the sternum for the abdomen is usually deep, with 

 the enclosing margin rounded either side; but in the Sooloo species 

 (and also Say's Monolepis inermis), the channel has a prominent tren- 

 chant margin. The outer maxillipeds in the Megalopidea are not in 

 contact; the third joint is considerably shorter than the first, yet 

 sometimes a little oblong ; the second joint is truncate at top. The 

 palpus is without a multiarticulate flagellum, a single, rather short 

 joint occupying its place. The second pair of maxillipeds has an 

 elongate one or two-jointed extremity to the palpus ; while the main 

 stem is narrow, with the terminal joints also narrow and short. 



The eight posterior legs are all rather slender, with the second 

 usually shorter than the third, and the fifth the shortest. The fifth 

 in Megalopa terminates in a tarsus like that of the preceding pairs of 

 legs, being so described and figured by different authors. In Mono- 

 lepis, the tarsus of the fifth pair is styliform, but bears at extremity 

 three or four serrate or setulose setaa, longer than the tarsus, the 

 presence of these seta? being one of the peculiarities of the genus, dis- 

 tinguishing it from Megalopa, according to Edwards.* In Cyllene, 

 this joint is lamellar, with some longish setge towards the extremity. 

 In Tribola, it is simple styliform, without long setse, as in Megalopa. 



The species of Cyllene collected by us, have a recurved spine on 

 the under side of the basal joint of the eight posterior legs, like Meg. 

 Montagui and armata of Leach, besides being similar to them, also, in 



* Crust., ii. 263. 



