400 ARACHNOIDEA 



oped and carried across the front of the body; eye stalks very long and 

 slender; color light brown, mottled with purple and dark brown: small, 

 active crabs, living in burrows, often a foot or two deep, in salt marshes 

 and on mud and sand flats ; they are frequently seen in large droves, and 

 have the habit of slowly waving the large claw back and forth, probably 

 a threatening attitude; numerous species; cos- 

 mopolitan; about 7 American species. 



U. pugnax (S. I. Smith). Inner surface of 

 large claw with an oblique ridge, beneath which 

 are granules; length of carapace 15 mm.; width 



^^^' {PauimeitrT'''^'' ^^ ^^'' ^^P® ^^^ *° Florida; common in salt 

 marshes. 



U. minax (Le Conte) (Fig. 638). Legs with red patches at the 

 articulations; large claws wdth an oblique ridge on the inner surface; 

 length of carapace 25 mm.; width 38 mm.: Cape Cod to Florida; the 

 largest of the fiddlers, common in salt marshes, usually farther from 

 the sea than the other species, being frequently where the water is 

 fresh. 



U. pugilator (Bosc). Length of carapace 15 mm.; width 21 mm.; 

 inner surface of large claw without oblique ridge: Cape Cod to Florida, 

 on sandy or muddy beaches near high-water mark. 



Class 2. ARACHNOIDEA. 



Arthropods without antennae, in which the body is usually made 

 up of two divisions, the cephalothorax and the abdomen, the former rep- 

 resenting the fused head and thorax and bearing six pairs of appendages, 

 and the latter being in most cases without appendages. The class con- 

 tains 2 subclasses. 



Key to the subclasses of Arachnoidea: 



Oi Marine arachnoids of large size, with appendages bearing gills on the 



abdomen, and a long spike-like telson 1. Xiphosura 



aa Mostly terrestrial arachnoids without abdominal appendages. .2. Araciinida 



Subclass 1. XIPHOSURA.* 



King or horseshoe crabs. Large crab-like arachnoids, in which the 

 body consists of a cephalothorax, an abdomen, and a long spike-like tel- 

 son or tail. The cephalothorax is horseshoe-shaped and unsegmented 

 and with an arched dorsal surface, in the center of the ventral surface 

 of which is tlie mouth. Six pairs of elongate appendages surround the 

 mouth, the anterior five of which are chelate, the sixth pair terminating 



* See "Xiphosura," Camb. Nat. Hist,, Vol. 4, p. 259, 1909. 



