1400 



CRUSTACEA. 



Seventh. The inner antennas losing their fossettes, and being con- 

 stantly exsert. 



Eighth. The branchiae being more than nine in number on either 

 side. 



The first of these peculiarities distinguishes many of the Grapsoids, 

 as well as lower species. The second is observed in the Corystoids, 

 and is an additional mark of their inferior grade. The third occurs 

 in Dromia and allied. The fourth, in Latreillia. The fifth, in 

 Dromia. Dromia and Latreillia have the posterior legs abbreviated, 

 and in Dromia, this evidence of degradation is still stronger, in that 

 the fourth as well as fifth pair is short and dorsal. 



The last three characteristics, above mentioned, mark a transition 

 towards the Macroural type, and the genera of this kind belong with 

 the Anomoura. This transition is seen further in — 



Ninth. The eyes being without fossettes. 



Tenth. The second pair of antennas becoming exterior to the eyes. 

 Eleventh. The outer maxillipecls more enlarged and subpediform. 

 Twelfth. The abdomen more lax and furnished with a pair of caudal 

 appendages. 



Thirteenth. The abdomen more elongated, and hardly inflexed. 



These several changes exhibit a continuation of the process of re- 

 laxation in the central forces. There is thereby an enlargement of the 

 antennas, and their more remote position at the anterior extremity of 

 the animal; and also, an enlargement of the posterior or abdominal 

 parts of the animal, and a development of appendages in the posterior 

 direction. These marks of degradation, excejsting the thirteenth, are 

 found in the Hippa and Porcellana groups, and the thirteenth in the 

 Paguridea. At the same time that these Macroural characteristics 

 appear, the body becomes elongated. The species all bear a stamp of 

 imperfection in the abbreviated posterior legs, as explained above, as 

 well as in the other points alluded to. The subordination of the nine 

 anterior annuli to cephalic functions, which is so striking in the Maioids, 

 has become less and less complete, and the organs less perfect ; more- 

 over, the habits of the animals are more sluggish, and they are less 

 fitted for self-preservation. The large Dromia picks up a waste shell, 

 and by means of its hind legs, lifts it over its body for protection, and 

 the Pagurus finds shelter in the water-worn univalves of a coast. 



