782 



ARTHROPODA 



PHYLUM VII 



prototype from which later Eurypterids are descended. Cambrian (Potosi 

 limestone) ; Missouri. 



Eurijpterus Dekay (Lepidoderma Reuss ; (?) Ctwipylocejjhalus Eichw.) (Figs. 

 1505, 1506, 1508). Body elongate, narrow, attaining sometimes a length of 

 1 m. Prosoma contained five or six times in total length of the body, depressed 

 convex, subquadrate, with rounded anterior angles. Anterior margin nearly 

 straight, posterior slightly concave. Eyes reniform, somewhat in front of the 

 middle ; between them and close to the axial line are two ocelli. The entire 

 prosoma bordered by a narrow marginal furrow, and the margin broadly 

 enfolded on the ventral side. In the middle of the lower side is the cleft- 

 shaped mouth, which is bordered laterally by the basal segments of the fifth 

 pair of legs, and posteriorly by the large oval metastoma. Ordovician 

 (Normanskill shale) to Permian ; Europe and North America. 



The first pair of ap])endages was regarded by Woodward and Schmidt as filiform and 

 tactile. Laurie, Holm, Clarke and Ruedemann, and others, however, have shown that they 

 are chelicerate, and thus in accord with homologous structures in other members of the 

 family. The three succeeding appendages are six- or eight-jointed and covered with fine 

 spines. The fifth pair is eight-jointed, and longer than those in front of it. The posterior 

 pair is a powerful swimming-organ ; its great subquadrate basal joints enclose the metastoma, 

 and together with this, cover nearly one-half of the ventral side of the prosoma. 



All of the body segments are free. The first six form the mesosoma, and together 

 collectively occupy about one-fourth of the body-length. They are short and broad, and 

 nearly uniform in shape ; but the second segment has lost its hard skeleton on the ventral 

 surface, and the first covers the greater part of the genital operculum. This first segment 



joins the jjosterior margin of the prosoma 

 and consists of two lateral portions and 

 a median process. All six segments of 

 the mesosoma are moderately overlap- 

 ping on the ventral side, and each is 

 divided by a median suture or cleft into 

 two parts. After these follow the six 

 ring -like segments of the metasoma, 

 which diminish gradually in width pos- 

 teriorly, and the body is terminated by 

 a long, slender telson. The latter is 

 properly to be regarded as an appendage 

 of the twelfth segment, as indicated by 

 the position of the anus in relation to it. 

 Larval stages have the telson short, 

 thick and four-sided, witli dorsal, ventral 

 and two lateral edges, corresponding in 

 form to that of the primitive Strabops. 



About twenty-five species of Em'yj)- 

 f.rrus are known, the largest being about 

 1 m. long. They are found for the most 

 part in argillaceous or sandy deposits 

 in transition strata between tlie Silurian 

 and Devonian of England, Gotland, 

 Oesel, Podolia, and in the Water-lime 

 Grou]) (Silurian) of New York. They 

 are rare in the Devonian, but occur 

 again more frequently in the Coal 

 Measures of Scotland, Silesia, Bohemia, 

 Saarbriicken, and Pennsylvania. The 

 last survivor is from the Permian of 

 Bussaco, Portugal, where it occurs in 

 association witli land plants {JValchin, Sphenopteris). Typo, E. re7)iipes Deka.y . 



Onyc]iop)ierns Clarke and Ruedemann. Terminal claw (with joint) of sixth 

 leg developed into a propelling spine ; fifth pair undifferentiated. Silurian ; 

 Indiana. Type, Eurypterus kokomoensis Miller and Gurley. 



Fio. 1508. 



Eurypterus rem.iiies Dekay. Bertie AVaterlime (Silurian); 

 BuH'alo, N.Y. Ventral aspect of a young individual in 

 which tlie relatively large size and length of the paddles, 

 and abrupt contraction of the body posteriorly, are especi- 

 ally noteworthy, x 3/j (after Clarke). 



