Mr. H. Woodward on the Structure of the Xiphosura. 545 



beds containing Ammonites Bucklandi, Gryphcea incurva, Lima gi- 

 gantea, &c, and which has been named the Infra-lias ; (2) that the 

 Mollusca and certain well-known species of Madreporaria, which 

 are grouped together at Brocastle, have similar relations to each 

 other in the Calcaire de Valogne, in the zone of Ammonites Moreanus 

 of the Cote d'Or, and in the Gres de Luxembourg ; and (3) that 

 the above-mentioned beds in Wales, constituting a coralliferous 

 horizon, are the equivalents of the Upper beds of the French and 

 Luxembourgian Infra-lias. 



3. " On some points in the structure of the Xiphosura, having 

 reference to their relationship with the Eurypterida." By Henry- 

 Woodward, Esq., F.G.S., F.Z.S., of the British Museum. 



The author pointed out that Prof. M' Coy's tribe Poecilopoda was 

 intended to include the Limuli, with Eurypierus, Pterygotus, and 

 Belinurus. Prof. Huxley had already shown (in 1859) that this 

 classification was founded upon an erroneous interpretation of the 

 fossils, then (1849) only known in England by extremely frag- 

 mentary remains. 



The object of this communication was to demonstrate that although 

 Prof. M' Coy's classification was based on conjecture rather than 

 upon a minute acquaintance with the anatomy of these extinct forms, 

 yet the subsequent researches of Profs. Agassiz and Hall in America, 

 Prof. Nieszkowski in Russia, and the independent investigations of 

 Mr. J. W. Salter and the author in this country have shown that a 

 close relationship actually does exist between the Xiphosura and 

 the Eurypterida. 



The author then gave a detailed comparison of the structure of 

 these two divisons, which he proposed to call suborders of Dr. Dana's 

 order Merostomata, He also pointed out that the Xiphosura were 

 divisable into three genera : — 1st, Belinurus, Baily, having 5 freely 

 articulated thoracic segments, and 3 anchylosed abdominal ones and 

 a telson ; 2nd, Prestwichia, a new genus, having the thoracic and 

 abdominal segments anchylosed together ; and 3rd, Limulus, Miiller, 

 having a head composed of 7 cephalic and 1 thoracic segments, 

 followed by 5 coalesced thoracic somites bearing branchiae, and 1 or 

 more coalesced apodal abdominal somites, to which is articulated 

 the telson. Although so great a dissimilarity exists between Ptery- 

 gotus and Limulus, yet in the genera Hemiaspis, Exapinurus, and 

 Pseudoniscus we have forms which, in the number of body-rings, 

 are intermediate. 



The order Merostomata offers a parallel group to the Decapoda, 

 the Eurypterida representing the Macrura, and the Xiphosura the 

 Brachyura. The author did not, however, intend by this comparison 

 to indicate that Limulus was higher in the Crustacean scale than 

 Pterygotus, but rather that the former was one of those low but 

 persistent types (like the Brachiopoda) which have remained un- 

 changed through long geological ages, whilst forms capable of 

 further development, like Pterygotus, have been modified and swept 

 away. 



Phil. Mag. S. 4. No. 219. Suppl. Vol. 32. 2 N 



