DECAPODA. 



515 



Oc-- 



Pt.s--- 



Fk8- 



Eryonidae and Scyllaridae there is no pleural fold at this part 

 to separate the epistome from the sides of the carapace. 



In the large group 

 of the Anomura the 

 pterygostomial region 

 is separated from the 

 carapace by a distinct 

 and flexible suture (6-) 

 and forms a movable 

 flap, which anteriorly 

 projects freely at the 

 sides of the epistome 

 (Fig. 315). In the 

 notch between this 

 and the forward con- 

 tinuation of the 

 pleural fold is set the 

 second antenna. This 

 is the relationship of 

 the parts character- 

 istic of the Anomura. 



In the Brachyura 

 the anterior part of 

 the epistome is differ- 

 entiated fro m the 

 deeply excavated pos- 

 terior part, and bears 

 the first and second 

 antennae on its front 

 border. The pterygostomial region, although marked off in 

 the Brachyura, from the rest of the carapace by the pleural 

 suture, is not movable on it.* Anteriorly it abuts against 

 the sides of the front part of the epistome, and, instead of 

 projecting freely, joins with the latter by a suture (Fig. 

 316). This suture is most marked in the lowest group of the 

 Brachyura, the Dromiidae. The ridge forming its outer border 

 may be regarded as the pleural margin of the carapace. 



* Its free margin forms the side of what is known as the buccal frame, 

 limiting the recess in which the mouth parts are contained. This recess 

 ie closed by the door-like third maxillipeds (Fig. 316). 



FIG. 315. Munida showing the relations of the pterygo- 

 stomial region to the epistome in the Anomura. anti first 

 antenna ; ant 2 second antenna ; Ch chelipeds ; Ep 

 epistome ; Mn cutting edge of the mandible ; Mxp s 

 pediform third maxilliped ; Oc eye ; Pl.s pterygostomial 

 flap ; s pleural suture by which it articulates with the 

 carapace ; Th.8 slender last thoracic legs ; ul. upper lip 



