Dr. W. T. Calrtian — On Arthropleura Moyseyi, 7i.sp. 543 



80 closely the specimens of Arthropleura hitherto described that there 

 can be no doubt that Dr. Moysey was at least approximately correct 

 in referring it to that genus. Whether Andrea was right in supposing 

 it to be a young individual (other specimens referred to the genus 

 being of relatively gigantic size) is less certain. In any case the 

 details of the ornamentation seem to differ from all the described 

 forms, especially in the presence of two transverse tuberculated ridges 

 on each tergum, and in the fact that the ridges on the pleura are 

 nearer the anterior margin, and I propose, therefore, to regard it as 

 representing a new species. 



Systematic Positmi of Arthropleura. — The great importance of the 

 specimen here described lies in the fact that it gives, for the first 

 time, information regarding the general form of the body and the total 

 number of somites. In this individual the number of post-cephalic 

 somites cannot have been less than twenty-eight and may have been 

 more. This enables us to say with confidence that, whatever the 

 affinities of Arthropleura may be, it is certainly not an Isopod. 

 Andree, who has recently discussed the systematic position of the 

 genus, comes to tlie remarkable conclusion "das in der Arthropleura 

 ein Isopoden-Typus vorlage, bei welchem die Sonderung in Thorakal- 

 und Abdominalsegraente noch nicht erfolgt ist".' It is very difficult 

 to discover, in the course of Andree's two lengthy memoirs, on what 

 conceptions of Malacostracan phylogeny this conclusion is based. It 

 can hardly be seriously contended nowadays that the Isopoda are the 

 most primitive group of the Malacostraca, and that all the other 

 Orders have been derived from them ; the alternative hypothesis, 

 which Andree in certain passages seems to adopt, is that the common 

 characters of the Malacostraca — the fixed number of somites, the de- 

 limitation of thorax and abdomen, and so forth — have been acquired 

 by the Isopoda independently of the other Malacostraca. This view 

 will hardly commend itself to anyone who realizes how many struc- 

 tural characters link the Isopoda, by way of the Tanaidacea, with the 

 Cumacea and the Mysidacea. 



The resemblances between Arthropleura and the Devonian Oxyuro- 

 poda were pointed out by Carpenter & Swain in their paper on the 

 latter genus,'' and more fully by Andree.' If it be admitted, there- 

 fore, that Arthropleura is no Isopod, the doubts that have been cast on 

 the Isopodan nature of Oxyuropoda gain in strength. 



The characters of Arthropleura, and more especially the very 

 remarkable structure of the sternal surface as described by Kliver* 

 and by Boule,^ seem to have no close parallel among recent 

 Arthropoda. It may be a Crustacean of a type hitherto unknown, it 

 may even be a very generalized and primitive kind of Myriopod ; 

 but our present knowledge does not seem to justify any more definite 



^ PalcEontographica, Ivii, p. 86, 1910 (" that in Arthropleura we have an 

 Isopod type in which the separation into thoracic and abdominal segments has 

 not yet taken place ")• 



2 Proc. Roy. Irish Acad., xxvii, B (3), p. 65, 1908. 



' Palceontographica, Ivii, p. 92, 1910. 



* Palceontographica, xxxi, p. 14, pl. iv, 1884. 



' Bull. Soc. Industrie Min^rale, St. Etienne (3), vii (4), p. 630, pl. Iv, 1893. 



