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 Palinuride 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 a: P. trigonus P. vulgaris e interruptus and 
P. edwardsii A A all other longicorn 
P. hiigelii. species 
A 
Rostrum large | 
r 
ophthal ; 
| erage nt. Rostrum re- | ; 
Pedate processes, de- ` \ ; duced to a 
n d en nee si small spini- Rostrum atrophied : 
meral plates, clasp the >form tu- ————-> coxocerites p ly 
base o rost bercle fu ig 
other characters as sternum n 
in x. antennulary Ruga 
apis elongate 
Stridulating organ Toa 
| developed : rostrum E 
‘> more or less reduced: d 
procephalic processes 
atrophied : ot 
characters as in x. 
PARENT SPECIE 
No sevilla tity organ : 
rostrum well developed: 
procephalic processes 
rit 
antennulary flag sia 
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 Palinuride from a brief notice of 
a paper by Boas (Studier over Decapodernes Slaegtskabsforhold) in the ‘ Zoological 
Record for 1880,” p. (Crust.) 32. 
