THE EURYPTERIDA AND XIPHOSURA COMPARED. 183 



belonging to the genus BeUinurus, Konig, with descriptions of two new species from 

 Queen's County, Ireland." 1 Mr. Baily points out the importance of maintaining Konig's 

 genus BeUinurus? which had been set aside by Buckland, in his ' Bridgewater Treatise,' 

 who referred this Coal-measure form to the modern genus Limulus. 3 He defines them 

 as Entomostraca of the legion Pcecilopoda, and order Xiphosura. Mr. Baily also 

 approves and cites Pictet's arrangement, who places Limulus, Halycine, BeUinurus, and 

 Pterygotus in the order Xiphosura.* 



In a communication to the Geological Society in 1866, 5 I have endeavoured to show 

 the grounds upon which my classification of the Eurypterida and Xiphosura in the order 

 Merostomata is based ; and it may perhaps be desirable before proceeding with the 

 descriptions of the genera and species belonging to the remaining sub-order, briefly to 

 recapitulate the reasons for adopting and adhering to it. 



The Sub-orders Eurypterida and Xiphosura compared. 



I. — In the division of the Merostomata, already described, we have seen that in 

 Pterygotus (Part I, PI. VIII) and Eurypterus (Part IV, p. 132, woodcut, fig. 40) the animal 

 consists of a more or less semicircular head-shield (cep/ialon, Bates ; 6 cephaletron, Owen 7 ), 

 bearing in the centre the ocelli, and also a larger pair of marginal or subcentral com- 

 pound eyes upon its dorsal aspect ; whilst beneath, upon its ventral aspect, we find the 

 oral aperture, in front of which arise a pair of chelate (in Pterygotus) or simple antennas 

 (in Eurypterus, Slimonia, 8 and Stylonurus^) , followed by three pairs of more or less 

 slender monodactylous pedipalps, and lastly, by a pair of very broad (spatulate) and 

 powerful swimming-feet, whose basal joints subserve the office of mandibles and maxillae. 



The general arrangement of these oral appendages is alike in all the Eurypterida 

 save that in Pterygotus, in which the antennas are chelate (serving as powerful organs of 

 prehension) ; the basal joint does not subserve the function of manducation, but in 

 Slimonia (Part III, PI XVII, fig. 3), Stylonurus (Part IV, p. 131, fig. 39), and 

 Eurypterus (Part IV, p. 132, fig. 40), in which the antennas are small and simple, the 



1 See 'Ann. and Mag. Nat. Hist.,' 1863, 3rd series, vol. xi, p. 107, pi. v. 



2 Konig's ' Icones Fossilium Sectiles,' 1820, pi. xviii, fig. 230. 



3 Buckland's ' Bridgewater Treatise,' 1836, vol. i, p. 396, vol. ii, p. 77, pi. xlvi", fig. 3. 



4 Pictet's 'Traite de Paleontologie,' ed. 2, 1854. 



5 See 'On some points in the Structure of the Xiphosura having reference to their Relationship with 

 the Eurypterida,' by H. Woodward, 18/6, vol. xxiii, p. 28, pis. i and ii (read November 21st, 1866). 



6 See Introduction, Part I, p. 5. 



7 See ' Anatomy of the American King-Crab (Limulus poly •phemus) ,' 1873, by Prof. Owen, F.R.S., 

 p. 463 ; 'Trans. Linnean Soc.,' vol. xxviii, part iii. 



8 See ante, Part III, p. 109, fig. 31. 



9 See ante, Part IV, p. 131, fig. 39. 



