6 J. D. Dana on the Classification of Crustacea. 
the preceding, producing lower grades of species. "They are ali 
marks of a relaxation of the centralization. 
Fourth. An enlargement or widening of the sternum and ab- 
domen. 
Fh. The abdomen becoming somewhat relaxed from the 
venter instead of remaining close-appressed to it. 
Sixth. 'The vulvse becoming more remote from one another, 
being situated in the bases of the third pair of legs, instead of 
the sternum. 
ASeventh. ''he inner antenns losing their fossettes, and being 
constantly exsert. 
Jghth. ''he branchise being more than nine in numbe: 
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 oceurs 1n Drom?a and allied. The fourth, in. Latreillia. 
The fifth, in Dromia.  Dromia and Latreilia have the posterior 
legs abbreviated, and in Dromia, this evidence of degradation is 
bes stronger, in that the fourth as well as fifth pair 1s short and 
orsal. 
The last three characteristies, above mentioned, mark a tran- 
sition towards the Maocroural type, and the genera of this kind 
belong with the Anomoura. "T'his transition is seen further in— 
Ninth. 'The eyes being without fossettes. 
Tenth. ''he second. pair of antennze becoming exterior to the 
es. ; 
Eleventh. 'The outer maxillpeds more enlarged and subpe- 
diform. 
Twelfih. ''he abdomen more lax and furnished with a pair of 
caudal appendages. 
Tirteenth. 'The abdomen more elongated, and hardly inflexed. 
These several changes exhibit a continuation of the process of 
relaxation in the central forces. 'lhere is thereby an enlarge- 
ment of the antennes, and their more remote position at the an- 
tenor 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. "lhese marks of de- 
gradation, excepting the thirteenth, are found in the Hippa and 
Porcellana groups, and the thirteenth in the Paguridea. At the 
same time that these Macroural charaeteristics 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 cephalie functions, which is so striking in the 
Maioids, has become less and less complete, and the organs less 
perfect; moreover, the habits of the animals are more sluggish, 
