BRACHYURA. 423 



similarly small examples. Goniocaphyra incequalis, Rath bun, is, I believe, a 

 synonym her photograph gives an excellent impression of the present specimen. 

 The preceding table shows comparative characters in these forms. Alcock's description 

 was based on 19 specimens from various localities. His measurements refer to 

 Mauritius specimens in particular. A. Milne-Edwards' "type"- specimen was large 

 (C.b. = 23 -00). 



Goniocaphyra incequalis comes under Catoptrus nitidus as described by Alcock 

 except as regards characters (6) and (7) of table, and of these (7) is admittedly variable 

 (even in Miss Rathbun's photograph there seems to be some indication of a proximal 

 tubercle). My specimen is intermediate in regard to character 6. 



Dr. de Man points out ('Notes, Leyden Mus.,' xii., p. 67, 1890) that his Gonio- 

 caphyra truncatifrons is young and = Catoptrus nitidus. The evidence suggests a 

 single species for the forms included in the table, within which de Man's truncatifrons 

 specimen stands somewhat apart. 



Mertonia, n. gen. 



Description : Carapace rudely semicircular in outline, the posterior border being 

 the longest, and the postero-lateral borders anteriorly convergent, to form a common 

 curve with the well-arched antero-lateral and anterior borders ; it is but little broader 

 than long, is convex fore and aft, and strongly declivous anteriorly. Regional 

 distinctions are almost imperceptible. Fronto-orbital border more than one-half 

 (about - 6 in the two specimens), and front one-quarter, the greatest breadth of the 

 carapace ; front is prominent and bilobed. 



Orbits somewhat ventral, completely filled by immovable elongated eye-stalks ; 

 eyes small. 



Antennules small ; they fold obliquely into proper pits. 



Basal antennal segment fairly long, its antero-external angle stands well in the 

 orbital hiatus ; the anterior portion of the hiatus is occupied by the flagellum, which 

 is stout and markedly plumed and half the carapace length. 



The epistomial wall of the buccal cavern is well formed and prominent ; the buccal 

 cavern is not completely closed by the external maxillipeds, a considerable space being 

 left between their inner borders, particularly those of the meri ; the flagellum articulates 

 with the antero-internal angle of the merus ; the antero-external angle of the merus 

 is produced. 



Chelipeds a little unequal, much more massive than, but about the same length as, 

 the 3rd pair of walking legs ; palm short, deep, and compressed, with sharp edges. 



Walking legs slender, unarmed ; dactylopodites styliform : the 3rd and 4th pair of 

 approximately equal length (the 2nd pair missing). 



For key purposes Mertonia comes under division I. l.ii.b. of Alcock's key to the 

 Indian genera of the Rhizopinse (A. 6, p. 317). The other occupant of the same 

 division is Xeuoph thai modes, from which the new genus is distinguished readily by 



