Parxer.—On the Structure of the Head in Palinurus. 305 
There appear to be some interesting facts about the geographical distri- 
bution of the Palinuride, but my information is too scanty to allow of my 
doing more than glance at this part of the subject. I think there can be 
no doubt that all the longicorn species (Panulirus) agree in essential cha- 
racters with P. interruptus, but 1 can unfortunately obtain no definite in- 
formation as to two of the brevicorns, P. longimanus aud P. frontalis, and 
am, therefore, unable to say whether they should come under Jasus or 
under Palinurus, as restricted by me. 
Leaving these two species aside, it is worthy of remark that all the 
species of Jasus are confined to the Southern Hemisphere (Ethiopian and 
Australian Regions), and those of Palinurus, as restricted above, to the 
Northern Hemisphere (Palearctic Region), while those of Panulirus occur 
in both hemispheres, and, as far as I can make out, in all the zoo- 
geographical regions. 
* 
In concluding ‘this paper I wish to offer a few remarks on Mr. C. 
Chilton's views of the affinities of Palinurus, as set forth in his paper on 
Paranephrops in the last volume of these ‘‘ Transactions.” * 
Mr. Chilton says :—“ The most important result arising from the exami- 
nation of Paranephrops setosus is that its affinity to Palinurus now seems to 
be placed beyond doubt. Paranephrops and the Parastacide generally re- 
semble the Palinwride in that they have no appendages upon the first 
abdominal segment ; in this they differ from the crayfishes of the Northern 
Hemisphere, and from Homarus and Nephrops. The Palinuride and the 
Parastacide also agree in having hooked sete, while in the Potamobiide and 
the lobsters the sete are not hooked. Moreover the branchial formule of 
Palinurus and Paranephrops are almost identical. Taking the presence or 
absence of the first abdominal appendage as the basis of his classification, 
Professor Huxley placed the Palinuride and the Parastacide together as the 
Astyla, while the Potamobiide, Homaride, ete., together form the Stylophora. 
This classification is confirmed by the structure of the male reproductive 
organs in Paranephrops setosus, for these agree in every essential particular 
with those of Palinurus vulgaris as described by Brocchi. " After quoting 
Huxley's theory of the origin of Potamobiide and Parastacide from a 
common ancestor, distinguished as Protastacus, Chilton goes on to say 
“I have only to add that the Protastacus stock appears to have left 
Palinurus, which has lost the chelate limbs possessed by its $ncestors, as its 
marine representative in the Southern Hemisphere.” 
* On some Points of Difference between the English Crayfish (4stacus Auviatilis), 
and a New Zealand one (Paranephrops setosus), Trans. N.Z. Inst., vol. $v., p. 150. 
