DECAPODA REPTANTIA. 



PALINURA. 



The two tribes forming the Pahnura may be separated as 

 follows : — 



Antennal scale present ; first four pairs or 

 all five pairs of pereiopods chelate ; pleopods 

 present on first abdominal somite, . . Eryonidea. 



Antennal scale absent ; none of the pereio- 

 pods chelate, except occasionally the fifth pair 

 in the female ; pleopods absent from the first 

 abdominal somite, , . . . . . Scyllaridea. 



Tribe ERYONIDEA. 



Family ERYONIDAE. 



No specimens belonging to this family have previously been 

 recorded from British waters. Attention was first drawn to 

 these very peculiar Decapods by the Challenger expedition. 

 The honour, however, of being the first to describe one of the 

 group must be givea to Heller, who in 1862 described and figured 

 a small specimen of Polycheles typhlops from the Mediterranean. 

 No one seems to have attached much importance to this descrip- 

 tion until after the discovery of several allied species by the 

 Challenger, The capture of these specimens was amongst the 

 most remarkable results achieved by the expedition, as the 

 discovery of Polycheles and its ?llies was at least a partial fulfil- 

 ment of the hopes of those who maintained that, owing to the 

 unifoiTQity of conditions existing at great depths, there might 

 be found there organisms which had been regarded as extinct, 

 for the nearest relatives of Polycheles and Willemoesia are the 

 species of Eryon found in the Trias and Lower Cretaceous. 



Two genera have been taken in Irish waters, Polycheles (in- 

 cluding Pentacheles) , and Eryonicus. Willemoesia, which is 

 closely allied to Polycheles, is not yet known to occur within the 

 boundaries of the Irish marine area. 



The two genera are separable as follows : — 



Carapace depressed, the lateral borders very 

 sharply defined ; abdomen longer than cara- 

 pace, . . . e . . . . . . . . Polycheles. 



Carapace globular and inflated ; abdomen 

 shorter than carapace, .. .. .. Eryonicus. 



