ISOPODA. 17 



Eurydicidse and other neighbouring families, such as the Corallanidae, but in every one 

 of the mouth parts it presents some distinctive feature. It is at present represented 

 only by a single specimen of a single species, so that it is not possible to say what 

 amount of sexual dimorphism may occur. 



Argathona, n. gen. 



The characters of the family will at present suffice for those of the single genus. 

 Argathona is a nymph or half- goddess, so recently sprung from the brain of 

 Mr. Justin Huntly McCarthy, that her name is not likely to have been hitherto 

 borrowed for scientific purposes. 



Argathona normani, n. sp. Plate III. (A). 



The first peraeon segment is rather the longest, and the last rather the shortest. 

 The side-plates are diagonally furrowed, those of the second and third segments less 

 deep than the rest, and not produced beyond their segments ; the last four pairs are 

 rhomboidal. The fourth pleon segment overlaps the fifth at the sides. The telsonic 

 segment, with sinuous sides, becomes rather narrowly triangular as it approaches the 

 rounded apex. The dorsal surface of the animal from one end to the other is beset 

 with spines large or small, the only segment free from them being the first of the 

 pleon, but also a basal area is left free where one segment slides under another, and a 

 sinuous free area marks what is probably the boundary between the sixth pleon 

 segment and the true telson. The sixth and seventh segments of the peraeon have 

 each six pale tubercles among the fringing spines of the hind margin ; the fourth 

 pleon segment has the same number, but less regularly spaced ; the fifth has two 

 that are submedian and much larger than those already mentioned, and the sixth 

 segment has a pair which are quite near to the sides. The telson carries numerous 

 spines in the serrate border besides those that belong to the dorsal cover, and is 

 likewise fringed with long plumose setae. 



The eyes are dark, rather large, set wide apart. 



The short first antennae have the first and second joints apparently fused into one 

 thick joint, not much longer than the following more slender joint ; the flagellum, 

 rather longer than the peduncle, is twelve-jointed. 



The second antennae have the fourth joint rather longer than the three preceding 

 joints combined, and the fifth rather longer than the fourth ; the twenty-nine-joiuted 

 flagellum is once and two-thirds the length of the peduncle. 



The frontal lamina is pentagonal, not very large. The epistome forms two arms 

 widely divergent, reaching beyond the membranaceous upper lip, in which a trans- 

 verse area is perceptible of normal form, probably more highly chitinized than the 

 remainder of the appendage. 



The lower lip is longer than broad, the lobes elongate piriform, flattened on the 

 confronting margins, the rounded apices not as usual fringed with setules, but 



D 



