532 



Miss G. E. Webb on some 



Tlie appendages in both these stages are typically 

 Biuchyuran in character, the anteuiiular statocyst being 

 particularly well-developed (fig. 2). Tlie chief feature of 

 interest presented by the Megalopa is the size and position 

 of the last pair of thoracic legs. Tliese are much smaller 

 than tlie preceding pairs, and the inner margin of the last 

 joint or dactylopodite is not serrate, as in the other claws, 

 but quite smooth, and carries a terminal group of three long 

 setaj (fig. 1). This slender last pair of legs is more dorsal 

 than the others, and is carried bent forwards on the upper 

 surface of the carapace, often with the last three joints closely 

 flexed on the proximal joints. 



In the next stage (fig. 3) the fifth pair of legs is not 

 noticeably small in proportion to the other thoracic legs, nor 

 does it terminate in a group of setae ; it is, moreover, carried 



Fig. 3. 



First young stage. Dorsal view. Length of carapace =4*2 mm. 



extended laterally in a normal position, no longer bent up 

 over tlie back of the animal as in the preceding stage. 

 Evidently, therefore, tliis peculiar character of the fifth pair 

 of legs is confined solely to the megalopa stage of the life- 

 history; there is no trace of it in the adult crab. 



The small size and dorsal position of the fifth thoracic legs 

 in the adult is a character which is typical of certain groups 

 among the Brachyura. These are the Dromiacea; the Dorip- 

 pidai and lianinidae among the Oxystomata ; and thePalicidse 

 and Ptenoplacidse among the Brachygnatha. 



It is not so easy to determine how common this feature is 

 in the megalopa stage of the Brachyura, as the literature on 

 the larval stages is still very incomplete. 



It seem.Sj however, that the three main points comprised in 



