12 | eg [J ANUARE, 
dairof legs is the stouter, is of great weight, much greater than previous authors 
have recognised. In the Brachyura, the anterior pair is uniformly the strong 
pair ; and this uniformity through so extensive a group shows that the variations 
from it must be of importance in classification. This peculiarity of the Brachyura 
ls a consequence of the concentration of force in the cephalic or anterior portion . 
of the cephalothorax; and the diffusion of this force posteriorly, which in differ- 
ent degrees marks the Macroura, is especially exhibited in the legs. It is there- 
fore of no little interest to observe whether the first or the second pair is the 
larger, or whether the degradation is still greater and the 3d. pair is chelate like 
the 2d and even stouter, as in the Penzi. By regarding this character we are 
led to place Hippolyte and Rhyncocinetes with Alpheus, instead of with Palamon; 
also Hymenocera and Pontonia with Palemon, instead of with Alpheus; Pasi- 
phaa ina distinct group from the Penzi, &c. Moreover, the Penzinea, viewed 
in this light and stripped of some unrelated genera, make a natural group, for 
they are characterized by having the third pair of legs ZZe the second, instead of 
like the fourth. In the lowest forms among the Penzinea, there are z9 chelate 
or didactyle legs, and the species approach the Schizopods. 
In the preceding paragraphs we have but hinted at some of the more prominent 
principles involved in the classification of the Macroura here presented, a fuller 
exposition of which will be given in another place. Below is a synopsis 
of the arrangement thus arrived at, and following this synopsis, are our descrip- 
tions of new species. 
Synopsis Familiarum Crustaceorum Maecrowrorwum. 
I. THALASSINIDEA, vel MACOROURA PAGURO-SQUILLIDICA. 
Carapax suturà transversà notatus, posticeque szpe .suturis duabus longi- 
tudinalibus. Abdomen sepius multo elongatum. ^ Antennx externae squamà 
basali sive nullà sive parvulà instructz;. Pedes 2 antici prorsum projecti; 6 pos- 
tici habitu raro consimiles.  Spec?es fossores. 
LegioIl. THALASSINIDEA EUBRANCHIATA. 
Branchiis thoracicis instructa tantum. 
Fam. 1. Gxzsi».—Maxillipedes externi pediformes. Appendices caudales et 
alie abdominales lata. 
Fam.2. CarriaANAssIDE.—Maxillipedes externi operculiformes. Appendices 
caudales lata. j 
Fam.3. "TzarassINID;.—Maxillipedes externi pediformes. Appendices cau- 
dales lineares. 
Legio ll. THALASSINIDEA ANOMOBRANCHIATA. 
Il. ASTACIDEA vel MACROURA SUPERIORA. 
Carapax suturà transversà sepius notatus, lateribus anterioribus epistomate 
connatis. Antenna externe squamàá basalisive nullà sive parvà instruetz;. — Ab- 
domen sat breve vel mediocre. PBranchize penicillate. Pedes 2 antici oblique 
projecti; 6 postici directione consimiles. ! 
l. .AAntennc ecrterne squamá basali nom instructae. Pedes antici monodactyli. 
Fam. 1. SexvrzraRi»z.—Carapax valde depressus, marginibus lateralibus sat 
tenuibus, carapace lateraliter subito inflexo.  Antennz externae laminate, 
breves. Sternum trigonum. 
Fam.2. PariNuRip.-—Carapax subcylindricus, lateraliter late rotundatus. 
Antenne externe basi subcylindrice, longe. Sternum trigonum. 
2. Antenne externa squamü basali gnstnatip. Pedes antici didactyli. 
Fam. 3. Emvouipzx.—Carapax non oblongus, depressus, lateribus subito inflexis, 
abdomine multo angustiore. 
Fam. 4. Asra4cipnz.—Carapax oblongus, subcylindricus, abdomine parce angus- 
tiore. Sternum angustum. 
E d 
