78 Mr. R. I. Pocock on 



Chelipedes when extended reaching slightly beyond the 

 apex of the rostral spines ; merus cylindrical and armed above 

 with a single sharp spine situated at its distal extremity ; 

 manns cylindrical, furnished with an articular tubercle above 

 and below at its proximal end ; fingers slightly separated 

 basally when closed. 



Leys almost alike, differing principally in length, the first 

 pair being much the longest ; the segments are all simple and 

 cylindrical, the merus alone being armed distally with a sharp 

 spine ; this spine, very large on the first pair, becomes 

 gradually smaller from before backwards on the others, and 

 finally disappears on the fourth. 



Measurements in millimetres. — Length of carapac° (without 

 rostrum) 20^, width 14, width behind orbits 7 ; length of 

 rostral spine 12, of tooth from base Q>\ ; distance between apices 

 of spines 9£ ; length of chelipede 25, of first pair of legs 57^, 

 of last pair 26. 



A single specimen on Macclesfield Bank at a depth of 32 

 fathoms. 



Provisionally following Mr. Miers I refer to the genus 

 Naxia those species allied to Pisa and Hyastenus which are 

 characterized by the presence of an accessory spine or spinule 

 on each of the rostral projections. Thus restricted the genus 

 contains the species mentioned by Mr. Miers on p. 60 of his 

 Report on the Brachyura of the l Challenger,' and, in addi- 

 tion, two that are here added. Of these one is the species 

 described above, the other is N. eleyans, a species referred by 

 Mr. Miers {he. cit. p. 5S) to the genus Hyastenus. Whether 

 this species is more nearly allied to the typical Hyastenus 

 than to the typical Naxia it is difficult to say ; but at all 

 events it unquestionably possesses the rostral spinules by 

 which alone, according to Mr. Miers, the genus Naxia may 

 be separated from Pisa and Hyastenus. Curiously enough 

 these spines, which, although small, are very distinct, appear 

 to have been overlooked by both author and artist ; for no 

 mention is made of them in the description, and in the figure 

 that accompanies it no sign of them is to be detected. It is 

 very questionable whether a genus should be retained on so 

 slender a basis, and there appears to be but little doubt that 

 a revision of Pisa, Hyastenus, and Naxia will show that the 

 three can scarcely be regarded as distinct genera. It is for 

 convenience' sake alone that Naxia has been here restricted to 

 those few forms presenting an accessory rostral spine. The 

 following table will perhaps serve to show how these may be 

 separated from each other : — 



