CLASS II ARACHNIDA— XIPHOSURA 773 



centre in front. First pair of appendages chelicerate. Metastoma with two small 

 accessori/ plates. Abdomen with seven to ten segments, which are dorsally free er 

 coalesced ; the six anterior ones provided with lamellar appendages on the under side. 

 Telson long, ensiform, movahle. 



Family 1. Cyclidae Packard. 



Cephalothorax small, orhicular, discoidal or convex, calcareous or chitinous, 

 hounded hy a distinct border. Cephalic appendages nearly as in embryonic Limulus. 



Cyclus de Kon. (Fig. 1497). Known almost solely by the orbicular 

 cephalothorax with its imperfectly preserved appendages, which seem to be 

 simple swimming legs. Their enlarged joints cover the 

 ventral surface of the carapace everywhere except in J^^^^^^W^ 



the centre, which is occupied by a V-shaped plate, 

 towards the pointed extremity of which all the basal 

 joints of the limbs converge. Goal Measures ; Great 

 Britain, Illinois and Missouri. 



Family 2. Belinuridae Packard 



Fig. \m 



Cyclus americanus Pack. 

 Goal Measures ; Mazon Creek, 



Body limuloid in general aspect. Cephalothorax 

 rounded, with long, slender genal spines ; its a'ppendages as 

 in Idrval Limulus. Abdomen with the segments in part piinois. cephalothorax show- 



,^ -^ ingtracesoflegsandahmentary 



or almost wholly Consolidated ; telson of variable length. canai. Vi. 



Belinurus König (Fig. 1498). Gephalothorax hippocrepiform, its central 

 portion surrounded by a broad, flat marginal area, which at the genal angles 

 is produced into a long, slender spine. Abdomen with eight segments, 

 besides the much-elongated, slender telson ; seventh and eighth segments are 

 Consolidated. Upper Old Red Sandstone and Goal Measures of Great Britain 

 and northern France (B. bellulus König; B. reginae Baily). Also in Goal 

 Measures of Illinois {B. lacoei Packard). 



—Baily, W. II., Explanation of Sheet 137 of the Maps of the Geol. Surv. Scotland, 1859.— 

 Eemarks ou Belinurus. Ann. Mag. Nat. Hist, 1863, ser. 3, vol. xl— Giebel, O. G., Limulus 

 Decheni. Zeitschr. gesammt. Naturw., 1863, vol. xxi, — Meek, F. B., and Worthen, A. H., Rept. 

 Geol. Surv. 111., 1868, vol. iii. — Woodward, H., Notes on Neolinmlus, Cyclus, Merostomata, etc. 

 Geol. Mag., 1869-94, dec. 1, vol. v. ; dec. 3, vols. vii,, ix. ; dec. 4, vol. i. — Dohrn, A., Embryologie 

 und Morphologie des Limulus. Jeuaische Zeitschr., 1871, vol. vi. — Packard, A. S., Development 

 of Limulus. Mem. Boston Soc. Nat. Hist., 1872, vol. i. — Idem, Anatomy, Histology and 

 Embryology of Limulus. Anniv. Mem. Boston Soc. Nat. Hist., 1880. — Ideyn, Carboniferous 

 Xiphosurous Fauna of North America. Mem. Nat. Acad. Sei., 1885, vol. iii. — Van Beneden, 

 M. E., Systematic Position of King Crabs and Trilobites. Ann. Mag. Nat. Hist., 1872, ser. 4, 

 vol. ix. — Milne-Edioards, A., Recherches sur Tanatomie des Limules. Ann. Sei. Nat., 1873, 

 ser. 5, vol. xvii. — Lankester, E. R., Limulus an Arachnid. Quart. Journ. Microsc. Sei., 1881, 

 vol. xxi. — Peach, B. N., Further Researches among Crustacea and Arachnida. Trans. Roy. Soc. 

 Edinb., 1882, vol. xxx. — Williams, II. S., New Limuloid Crustacean from the Devonian. Amer. 

 Journ. Sei., 1885, ser. 3, vol. xxx.— Hall, J., and Clarke, J. M., Palaeontology of N.Y., 1888, 

 vol. vii. — Kishenouye, K., Development of Limulus. Journ. Coli. Sei. Tokyo, 1891, vol. v. — 

 Kinrjdey, J. >S., Embryology of Limulus. Journ. Morphol., 1892-93, vols. vii., viii. — Fritsch, 

 A., Fauna der Gaskohle. Prague, 1901, vol. \\.— Clarke, J. M., Pseudoniscus in the Eurypterus 

 Beds of New York. Rept. N.Y. State Palaeont. for 1900. (54th Ann. Rept. N.Y. State Mus.), 

 1902. — Rogers, A, F., Some new American Species of Cyclus from the Cqal Measures. Kansas 

 Univ. Sei. Bull., 1902, vol. i., No. 10. — Stromer von Reichenbach, E., Über Molukkenkrebse. 

 Zeitschr. Deutsch. Geol. Ges. Monatsber., 1907, vol. \ix. — Gaskell, W. II., Origin of the 

 Vertebrates, London, 1908. — Patten, W., Evolution of the Vertebrates and their Kin, 1912. 



