SUB-CLASS I MEROSTOMATA 673 
segments having a broad axis and lamellar pleurae with diagonal pleural lines; and a 
posterior portion (“abdomen ”) of four narrow segments, besides 
a long and acuminate tel on. Silurian; Oesel. 
Hemiaspis, Woodw. (Limuloides, Salter), (Fig. 1416). 
General form similar to Bunodes. Cephalothorax one-half as 
long as broad, with several genal spines; central portion well 
defined. Abdomen triangular, with nine segments besides a 
short telson. Abdominal axis broad, with a median ridge ; 
pleurae short and flat. Silurian; England. 
Bunodella, Matthew. Cephalothorax small, abdominal 
segments seven, acute. Axial portion of the body prominent ; 
telson not observed. Silurian; New Brunswick. 
Pseudoniscus, Nieszk. Body oval; cephalothorax short, 
with broad central portion and large compound eyes; nine 
trilobed abdominal segments besides a short caudal spine; the 
posterior ones nearly parallel with the telson. Silurian ; 
Oesel. 

Order 3. HURYPTERIDA. Burmeister. Fic. 1416. 
Fea, po 1 Hemiaspis limuloides, 
(Giga ntosti aca, Haeckel.) Woodw. Silurian; Leint- 
‘ : ne : wardine, England. 1/; (after 
Body elongated, with a thin chitinous epidermal skeleton Woodward). 
ornamented by fine scale-like markings. Cephalothorax usually 
with two large faceted lateral eyes and a pair of median ocelli ; on the ventral side with 
siz pairs of legs, of which the first is preoral and chelate. Mouth bordered posteriorly by 
a metastoma, and anteriorly by an epistoma, both simple plates. Abdomen thirteen- 
jointed, the anterior six segments bearing ventrally five pairs of broad, leaf-like appendages 
(apparently comparable to the operculum and branchial appendages of Limulus). The 
posterior six segments annular, without appendages ; telson sometimes spatulate in shape. 
This order, which is restricted wholly to the Palaeozoic, embraces the largest Arthropods 
known, some of them (Pterygotus, Stylonurus) having attained a length of over 2 metres. 
The presence of gills upon the branchial appendages shows that in all probability the 
Eurypterids were aquatic, and the structure of their appendages indicates that they were 
good swimmers. They are found associated with Graptolites, Cephalopods, and Trilobites in 

[} Literature : 
Dekay, J. E., On a Fossil Crustacean (Ann. N.Y. Lyceum Nat. Hist., I.), 1825.—Roemer, F. v., 
Ueber ein Eurypterus (Palaeontogr., I.), 1848.—J/‘Coy, F., Classification of some British Fossil . 
Crustacea (Ann. Mag. Nat. Hist. [2], IV.), 1849.—Hualey, T. H., On Himantopterus (Quar. Journ. 
Geol. Soc., XXI.), 1856.—Jdem, and Salter, J. W., On the Genus Pterygotus (Mem. Geol. Surv. 
United Kingdom Monogr., I.), 1859.—Page, D., Advanced Text-Book of Geology, 1856 and 1859.— 
Nieszkowski, J., De Euryptero remipedo. Dorpat, 1858. (Also in Arch, Naturgesch. Liv.-Esth. - 
und Kurlands, II.), 1859.—Hall, J., Palaeontology of New York, III., 1859.—Salter, J. W., Several 
Papers in Quar. Journ. Geol. Soc., XIX., 1863.— Woodward, H., Numerous Papers in Geol. Mag., I., 
1864 ; 1X., 1872; Quar. Journ. Geol. Soc., XXI., XXIV., XXVII., XXVIII., ete., 1865-72.—Jdem, 
Monograph of the British Fossil Crustacea of the Order Merostomata (Palaeont. Soc.), 1866-78.— 
Grote, A. R., and Pitt, W. H., New Species of Eusarcus and Pterygotus (Bull. Buffalo Soc, Nat. 
Sci., IIT.), 1875.—Pohlman, J., Fossils of the Water-Lime Group (ibid. IV., V.), 1882-97.—Peach, 
B. N., Further Researches among Crustacea and Arachnida (Trans, Roy. Soc., Edinburgh, XXX.), 
1882.—Schmidt, F., Miscellanea Silurica, III. (Mém. Acad. Imp. Sci., St. Pétersb. [7], XXXI.), 
1883.—Hall, J., Second Geol. Surv. Pennsylvania, Rep. PPP. 1884.—Whiteaves, J. F., Palaeozoic 
Fossils of Canada, III., Pt. 1, 1884.—Hall, J., and Clarke, J. M., Palaeontology of New York, VIL., 
1888.—Claypole, E. W., On Carcinosoma, etc. (Amer. Geol., VI., XIII.), 1890-94.—Fraipont, J., 
Eurypterides nouveaux du Dévonien (Ann. Soc. Geol. Belg., X VII.), 1890.— Laurie, M., Eurypterid 
Remains from Pentland Hills (Trans. Roy. Soc., Edinburgh, XX XVII.), 1892.—Anatomy and Rela- 
tions of Eurypterida (ibid.), XXXVIII.), 1893.—Recent Additions to Knowledge of Eurypterida 
(Nat. Sci., III.), 1893.— Whitfield, R. P., Report Geol. Survey of Ohio, VII., 1893.—Holm, G., 
Neue Bearbeitung des Eurypterus Fischeri (Bull. Acad. Imp. Sci., St. Pétersb. [5], IV.), 1896. 
VOL. I DES 
