PODOPHTHALMIA. 49 



the Hippidea and the Macroura; and we find these antennae longer as 

 the body passes from the transverse to the narrow elongate form. In 

 the broad Trichocera, they are but little longer than in some Can- 

 cridae ; but in Corystes, the length is as great as in Hippa, and the 

 organ is fringed with hairs through all its length.* We see in them, 

 therefore, the degraded Cancroid, and no resemblance to the Leuco- 

 soicls. Again, the outer maxillipeds are often prolonged over the epi- 

 stome, and as this is most striking in the narrower species which bear 

 other marks of degradation, this quality may be taken as another 

 proof of their inferior grade ; they approximate, in the ill-defined front 

 margin of the epistome, to the Macroura. 



This review of the relative rank of the different grand divisions of 

 the Brachyura, prepares us to trace farther the gradations through 

 the Anomoura to the Macroura. 



The peculiarities of the Macroura which should be in mind, are as 

 follows : — 



1. A large, elongate, extended abdomen, with five pairs of appen- 

 dages beneath, and another caudal pair (to the penult segment). 



2. Carapax, with rare exceptions, free at the side, and not soldered 

 anteriorly (as in the Brachyura) to the epistome. 



3. Inner antennae without fosse ttes, and elongated. 



4. Outer antennae posterior and often exterior to the eyes, elongated, 

 and often having a lamellar appendage at base. 



5. Front margin of buccal area not a distinct margin, and outer 

 maxillipeds pediform, instead of opercular. 



6. Vulvae in coxae of third pair of legs, and no copulative pouch. 



7. No sella turcica or median apodeme. 



8. The nervous cord elongated down the abdomen, and having a 

 series of ganglions. 



9. Branchiae usually more than nine in number. 



10. The carapax without a suture along the sides, but when any 

 exists, it crosses the middle of the back 3 that is, as has been explained 

 on a preceding page, the mandibular segment instead of forming only 

 the margin of the carapax either side, constitutes its posterior half 

 when any distinction of the segments is to be discovered. 



* It should not be understood that we consider small antennae a necessary mark of 

 higher grade; on the contrary, it is possible that the organs may be obsolescent, and BO 

 mark inferiority, as in Acanthocyclus. We allude only to a general principle, the point 

 of which must be obvious without further explanation. 



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