On the Classification of the Crustacea Chorisiopoda, 299 
racic legs of one side are obsolete excepting the 8 posterior, a fact 
pointing to the Amphipod arrangement 4:3.  Rathke's figure of the 
* Phryrzus Hippolytes"* represents a male with the 3 posterior legs 
either side thrown backward and the 4 anterior forward, confirming 
the same view. 
| In. Jone, there are thoracic branchial appendages, which is a wide 
divergence from the Isopoda. In view of these facts, we conclude that 
the Bopyri are properly Anisopods. "Dl he resemblance in habit to the 
Cymothoidze is no objection, for we find this habit also in the Cyami, 
species stili more remote. In fact, the male Bopyri show that ihe spe- 
cies in all essential points of structure, are nearest to J:era and Tanais. 
Moreover the Jzerze are mostly parasitic. 
The genera Crossurus, and Liriope of Rathket are near Tanais, 
though also related 'in form to male Bopyri. In Liriope the thoracic 
legs are grouped as in Tanais, and the abdominal appendages are sub. 
natatory or nearly Àmphipodan in structure, although, like "Tanais, 
diverse from true Amphipods in having 5 pairs subnatatory, and only 
one pair of stylets. | Liriope is referred to the Amphipoda by Rathke. 
Cryptothir is the name of another related genus, à species of. which 
was found by the author in the cavity of a living barnacle (Creusia). 
We iherefore adopt as the grand divisions of the Choristopoda, the 
three tribes, IsoropA, ANiIsoPoDA and AnwPHiPODA. 
It is an important fact, the basis of a philosophical principle, that the 
most sluggish aud most stupid of the Decapods are found in the transi- 
tion group, Anomoura. So in the Tetradecapods, the transition group, 
Anisopoda, contains those species of the order that are lowest in ac- 
tivity and structural perfection ; for the Bopyri, the females especially, 
when mature, are nearly memberless, motionless and senseless. 
The Zsopoda seem to have the same relation to the .AmpAipoda that 
the Brachyura have to the Macroura, and are the higher in rank. 
Tribe L. Zsopoda.—The Isopoda thus stripped of genera that are not 
properly of the tribe, are naturally divided into three subtribes, as 
follows :— | 
Subtribus L Iporxi»za.—Appendices abdominales duc postieze bene operculi- 
formes, appendices alias optime tegentes. 
Subtribus IL. OxrscorpzA.— A ppendices abdominales duc postiez styliformes et 
non operculiformes, fere terminales, raro obsoleta. 
Subtribus IIT. CvwornorpEA.—A ppendices abdominales dus: postez; lamellatz, 
apud abdominis latera disposita, 
Tribe 2. Anisopoda.—A mong the Anisopoda, we find the three sub- 
tribes of the Isopoda represented. Allied to the 7Zozeidea, there are 
Arctvrus, Leachia, Anthura; allied to the Onéscoidea, the genera 
Tanais, Apseudes, Bopyrus and others related; ailied to the Cymo- 
thoidea, the genera Serolis, Praniza, &c. Praniza is an aberrant form, 
abnormal in the number of its legs. "The three grand divisions are 
hence as follows :— 
Subtribus L. Segori»gA, vel Axwrsoropna Cvwormorca.—A ppendiees du: postic»e 
abdominales lamellate, apud abdominis latera dispositze. 
* Fauna Norwegens, pl. 2, f. 8. 1 Fauna Norwegens, pp. 38 and 60, pl. 1. 
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