Parker. — On the Structure of the Head in Palinurus. 



303 



Moreover P. vulgaris and P. trigonus are seen to be intermediate between 

 the species without a stridulating organ and the longicorns, approaching 

 more nearly, however — at least so it seems to me — to the latter, in virtue 

 of the possession of that mark of high specialization the stridulating organ. 



Assuming, as I think one is bound to do, that the Palinurida are 

 descended from some Astacine or Homarine ancestor, probably through 

 some such intermediate form as Palinurellus* one cannot but conclude that 

 the species which have no stridulating organ, a well-developed rostrum, 

 and imperfectly fused coxocerites come nearest to the primitive stock, and 

 that those species in which the stridulating organ is present, the rostrum 

 atrophoid, and the coxocerites completely fused, have undergone the widest 

 divergence from that stock and present us with the extreme of modification 

 of the Palinuroid type. 



These views may be conveniently expressed in the form of a phylogenetic 

 table, as follows : — 



P. lalandii 

 P. edwardsii 

 P. hilgelii. 

 A 



Pedate processes, de- 

 veloped from the epi- 

 meral plates, clasp the 

 base of the rostrum : 

 other characters as 

 in x. 

 A 



P. trigonus 

 A 



Kostrum large 

 enough to cover 

 ophthalmic 

 segment. 

 A 



P. vulgaris 

 A 



Rostrum re- 

 duced to a 

 small spini- 

 >form tu- — 

 bercle • 



P. interruptus and 

 all other iongicom 

 species 

 A 



Rostrum atrophied : 

 _> coxocerites perfectly 

 fused : antennulary 

 sternum widened : 

 antennulary flagella 

 elongated. 



Stridulating organ 



developed : rostrum 

 ,>P more or less reduced : 



procephalic processes 



atrophied : other 

 x. parent species. ' cha ™cters as in x. 

 No stridulating organ : ?j 

 rostrum well developed: 

 procephalic processes 

 present : coxocerites 

 imperfectly fused : 

 antennulary flagella 

 short. 



Assuming that this table is an accurate expression of the relationships 

 of the species of Palinurus, I think there can be no doubt that, in classify- 

 ing the species, the most important division must come along the line a b, 

 which divides the comparatively generalized non-stridulating forms from 



* I have unfortunately neither specimen nor description of this interesting genus, 

 and take the fact of its being the most primitive of the Palinuridcs from a brief notice of 

 a paper by Boas (Studier over Decapodernes Slaegtskabsforhold) in the " Zoological 

 Record for 1880," p. (Crust.) 32. 



