480 



CRUSTACEA. 



there are five pairs of long spiny legs, of which the last is much the 

 largest and ends in a broad swimming-fin. Some of the anterior 

 appendages may be armed with a chela. The resemblance of the true 

 Eurypt&ridai (in the general shape of their body) to the Scorpionidas 

 is very striking, while the genus Hemiaspis presents affinities to the 

 P&cilopoda. The most important forms are: Eurypterus p!/ 1 !"'" us 

 Salt., Devonian strata, Pteryyotus anylicus Ag., four feet long, from 

 the upper Silurian (fig. 373). 



FIG. $73.Eurypferus remipr-s fitter Xieszkowski. a, Dorsal view ; 6, ventral view ; O, eyes ; 



St. caudal spiiie ; H, kypostome. 



Order '2. XIPHOSURA.* 



Gigantostraca ivhose body, is divided into three parts, wJtich are 

 movably articulated together ; a large sliidd-sliaped cephalo-thorax, an 

 abdomen with Jive pairs of lamellar feet and a long movable caudal spine. 



The large body of these Crustacea is covered with a strong chiti- 



* 0. Gegeubaur, " Anatomische Untersuchung eincs Limulus, mit besonderer 

 Beriicksichtigung clcr Gcwebe," AWinndl. <!<> nntvrf orach. Gcst-lhdiaft zu 

 Hnllc, IV., 1858. Packard. "The Development of Limulus Polyphemus," Soc. 

 of \at. Hist., 1S70. A. M. Edwards. Itecherches sur 1'anatomie des Limules," 

 Ann. '. nut. V e Ser. Tom. XVII.. 1872-1873. [E. E. Lankester, "Limulus 

 au Arachnid, 7 ' Quart. Journ. Mic. Sue., vol. xxi.] 



