4SO 



CRUSTACEA. 



there are five pairs of long spiny leg.s, 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 

 Eurypteridce (in the general shape of their body) to the ticorpionidce 

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

 Pcecilopoda. The most important forms are: Eurypterus pygmceus 

 SaFt., Devonian strata, Pterygotus anglicus Ag., four feet long, from 

 the upper Silurian (fig. 373). 



FIG. 3~3.Euryptrrns remipfs after Nieszkowski. a, Dorsal view ; b, ventral view; O, eyes; 



Sf. caudal spine ; H, hypostome. 



Order 2. XIPHOSURA.* 



Giyantostraca ivhose body is divided into three parts, icJiich are 

 movably articulated together ; a large shield-shaped cephalo-thorax, an 

 abdomen with five jxtirs of lamellar feet and a long movable caudal spine. 



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



* C. Gcgcnbaur, " Anatomischc Untersuchung eincs Limulus, mit besonderer 

 Beriicksichtigung <1'T Gewcbe," AUmntJl. (?,> naturforxch. Gesi'lhcliaft zu 

 JfaUt', IV.. 1858. Packard. ''The Development of Limulus Polyphemus.' 1 Sue. 

 of Nttt Hint.. 1870. A. M. Edwards. ' Kcchcvchcs sur 1'anatomie dcs Liinules," 

 Ann. w. nat. V c Ser. Tom. XVII.. 1872-1873. [E. R. Lankestor, "Limulus 

 an Arachnid.'' Quart. Journ. Mir. Soc., vol. xxi.] 



