Parker. — On the Structure of the Head in Palinurus. 305 



There appear to be some interesting facts about the geographical distri- 

 bution of the Palinuridce, 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 (Pamdirus) agree in essential cha- 

 racters with P. interruptus, but I can unfortunately obtain no definite in- 

 formation as to two of the brevicorns, P. longimanus and 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 Eegions), and those of Palinurus, as restricted above, to the 

 Northern Hemisphere (Palasarctic Eegion), 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 Parastacidce generally re- 

 semble the Palinuridce 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 Palinuridce and the 

 Parastacidce, also agree in having hooked setae, while in the Potamobiidce and 

 the lobsters the setaa are not hooked. Moreover the branchial formulas 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 Palinuridce and the Parastacidce together as the 

 Astyla, while the Potamobiidce, Homaridce, etc., 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 Potamobiidce and Parastacida 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 ancestors, as its 

 marine representative in the Southern Hemisphere." 



* On some Points of Difference between the English Crayfish (Astacus fluviatilis), 

 and a New Zealand one (Paranephrops setosus), Trans. N.Z. Inst., vol. xv., p. 150. 

 20 



