PL .-€-—"r—m—UnBGSSESKNUCUHKROMRAACMPWNERTCEMST RU ME CUM T C i um9 RECS SM CSS ym 
298 On the Classification of the Crustacea. Choristopoda. 
mediate forms and are naturally arranged in a separate group. — T'hese 
constitute the tribe here named 
The AnisoPoDa. 
l. Like Amphlipoda, the three posterior pairs of thoracic legs are in 
one series, and the four anterior in a ud series or usually in 
ets of two patrs each ;—4(or 21-25: 3 
2. Like Isopoda, the three posterior pairs of abdominal members are not 
styliform, only the last pair being of this character; the branchial 
organs are abdominal and not thoracic; with a rare exception. 
These are constant characteristics of the whole group. Although 
stroog!y Amphipodan, the species have in general more external re- 
semblaüce to the Isopods; yet the intermediate character of some 
genera is so obvious that they have been arranged in the former group 
by oue author and in the lauter by another. 
'The genera that pertain to this tribe, Anisopoda, are the foltówitipl: 
Arcturus and the allied Anthura, Tiondns: Apseudes, Rhea, Pranixà, 
Anceus, Serolis, Bopyrus and allied... Each of the larger subdivisions of 
the [sopoda, as laid down by Edwards, affords one or more genera, and 
they are genera which in his system are in some instances marked off 
as anomalous in character. 
In Arcturus and Anthura, the thoracic members have the Amiphigód 
character, the series being 4 (of 2--9) :3, and not 3:4 as in the Isopods. 
The abdominal appendages are like those of Idotzea. 
In Tanais, there is the same arrangement. | The abdominal append- 
eges are Isopodan in being characterized by the series 5: 1, but the 5 
anterior are elongated and subnatatory, the abdomen is more flexibly 
articulated, approximating to the Amphipods; the 6th pair is a pair of 
stylets. Apseudes and KAa«a are closely like Tanais, &nd actually more 
resemble Amphipods than Isopods. "T'he abdomen is more elongated, 
and differs from the Amphipodan abdomen mainly in having but one 
pair of stylets with 5 pairs of subnatatories instead of three of stylets 
and three of natatories. 
Praniza and Anceus have the thoracic legs Amphipodan i in their ar- 
rangement. 'lhe abdomen in Praniza is considerably elongated and 
flexible, approaching the Amphipodan ; but the arrangement Lof i its ap- 
pendages is Isopodan. 
In Serolis, althovgh the general aspect of the species is strikingly 
Isopodan, the arrangement of the thoracic legs is Amphipodan. — Fur- 
ther than this, the abdomen is partly Amphipodan, for instead of the 
series 5: I, it has the series 8:3; yet while the 3 anterior pairs are 
natatory as in the ÀÁmphipoda, the next two, instead of being styliform, 
like the last, are branchial (one opercular to the other), and in this par- 
ticular they are Isopodan. 
In the Bopyri, the thoracic legs are so arranged in a single continu 
ous series, that it is difficult to make out ihe series 4:3 0r 8:4. Yet in 
some figures, the former (the Amphipodan) arrangement is indicated. 
The males are closely like Tanais in some instances, both in the length 
of the abdomen, its free articulations and its appendages.* Ina female 
not adult of the Bopyrus abdominalis, figured by Kroyer;f all the tho- 
* See Króyer, in Voy. Scand, pl. 28, ig. 1.A., DDojus Mysidis. — 1 Ibid. pl. 29, fip. 17. 
