CRUSTACEA. 



ORDER II. 



P^ECILOPODA*. 



THE Paecilopoda are distinguished from the Branchiopoda by the diversity in 

 the form of their feet, among the anterior of which an indeterminate 

 number are ambulatory, or fitted for prehension ; while the others, 

 lamelliform or pinnate, are branchial and natatory. It is principally, 

 however, by the absence of the usual mandibles and jaws that they 

 are removed from all other Crustacea. Sometimes these parts are 

 replaced by the spinous haunches of the first six pairs of feet ; and 

 sometimes the organs of manducation consist either of an external 

 siphon in the form of an inarticulate>l rostrum, or of some other 

 apparatus fitted for suction, but concealed or slightly apparent. 



Their body is almost always, either wholly or for the greater por- 

 tion, invested with a shell in the form of a shield, consisting of a 

 single plate in most of them, and of two in others, which always 

 presents two eyes when those organs are distinct. Two of their antennae 

 Cheliceree, Lat form a forceps in several, and fulfil its functions. Most of 

 them have twelve feet, and nearly all the remainder have either ten or twenty- 

 two. Their usual habitat is on aquatic animals, and most commonly on 

 fishes. 



We divide this order into two families. 



FAMILY I. 



XYPHOSURA. 



THIS family is distinguished from the second by several characters : there 

 is no siphon ; the haunches of the first six pair of feet are covered with small 

 spines, and perform the office of jaws; there are twenty-two feet; the first 

 ten, with the exception of the two anterior ones in the males, are terminated 

 by a didactyle forceps, and inserted, as well as the two that follow, under a 

 large semilunar shield. They are wandering animals, and form the genus 



LIMULUS, Fabricius. 



The species are known in commerce by the name of the Molucca Crab. 

 These animals are sometimes found two feet in length, they inhabit the seas 

 of hot climates, and most generally frequent their shores. They appear to 



Various-footed. 



