360 PERCY SLADEN TRUST EXPEDITION 



second pair which may be fairly heavy ; dactylopodites of last three pairs usually simple 

 and slightly curved. 



Four distinct sections may be observed in PericUmenes. (l) P. aurantiaca (Dana) 

 differs sharply from all the rest in the lack of teeth on its rostrum. Quite possibly 

 further information will show that it should become the type of a new genus : for the 

 present it must have subgeneric rank. The remaining species fall into three groups. 



(2) In one of these the rostrum is rather short and has a convex upper edge, while the 

 second leg is unarmed and its wrist short. In this group the supraorbital spine is rare. 



(3) In another group, the dorsal edge of the rostrum is convex, and the second leg of the 

 only species in which this limb is known is short-wristed and unarmed, but the cornea, 

 which in all other PericUmenes is subhemispherical, is here ogival, and a strong supra- 

 orbital spine is present. (4) The remainder of the species, including more than half the 

 genus, form a group which is characterized by a rostrum with straight or concave upper 

 edge and tip nearly always upturned. The second leg generally bears a spine on arm 

 or wrist or both, and almost always has the wrist of a good length. The supraorbital 

 spine is common in this group. The existence of certain intermediate species, such as 

 P. commensalis Borradaile and P. amethysteus (Risso), makes it undesirable that these 

 sections should rank as genera. I have therefore established for them four subgenera, 

 named respectively Ensiger, Cristiger, Corniger, and Falciger'". The type species of the 

 genus belongs to Cristiger. 



Key to the subgenera of PericUmenes : 



I. Rostrum toothless. No spines on trunk or legs. 



Ensiger Borradaile, 1915. 



II. Rostrum toothed. Spines at certain points on trunk or legs. 



A. Cornea ogival. [Upper edge of rostrum convex. Strong supraorbital spine.] 



Corniger Borradaile, 1915. 



B. Cornea not ogival. 



1. Upper edge of rostrum convex. Second leg with short wrist, and unarmed, 



save that angles of wrist and arm are sharp in P. gracilis. Supraorbital 

 spine in one species only. 



Cristiger Borradaile, 1915. 



2. Upper edge of rostrum straight or concave. Second leg rarely with short 



wrist, generally with spine on wrist or arm or both. Supraorbital 



spine common. 



Falciger Borradaile, 1915. 



Subgenus Cristiger Borradaile, 1915. 



Ann. Mag. Nat. Hist. (8), xv. p. 207. 



Definition : Rostrum toothed, with convex upper edge, short or of medium length. 



Antennal and usually hepatic spines present. Supraorbital spine very rare. Second leg 



* Since these subgenera were established, in an article in the Annals and Magazine of Natural History 

 for February, 1915, I have learned that the names of two of them {Corniger and Falciger) are preoccupied 

 as designations of genera. They must, however, continue to stand as subgeneric names. 



