GM ND 2 
*- 
Mary J. Raikbua. 
: *i Ns 
v Ia A H 
—. From the American Journal of Scvnce and Arts, Second, Series, Vol. VIIT.—No. 22. 
: SYNOPSTS 
OF THE 
|. GENERA OF GAMMARACEA. 
By JAMES D. DANA. 
Tur tribe of Amphipoda among Crustacea includes the subtribes 
Gammaracea and Hyperiacea. "The former of these subtribes consists 
of six groups or families. 
Fam. 1l. OgcuEsTiDz.  Saltatorie. | Palpus mandibularis obsoletus. 
Corpus compressum, epimeris latis. Styli caudales duo postici breviores. 
Fam. 9. GamManIDx.  Saltatorize vel natatoriee. | Mandibulze palpi- 
gere. Corpus sepius compressum.  Anteun:e flagello confectze, non 
pediformes. Styli caudales duo postici sive longi sive breves. 
Fam. 3. CoRornHipu.  Gressorig. Corpus plus minusve depressum, 
lineare, abdomine recto, normali, epimeris angustissimis vel obsoletis. 
Mandibule palpigere. Antenne pediformes. 
Fam. 4. lcizirz. | Corpus depressum, latum, abdomine normali, in- 
flexo, pedibus laté expansis instar Aranezs.  Antennz non pediformes. 
Fam. 5. CHELUvRIDE. Corpus vix compressum. Abdomen abnor- 
male, segmentis duobus tribusve coalitis et irregularibus; stylis caudali- 
bus sex, dissimilibus. | Ántennza breves pediformes. 
Fam. 6. DuricHipz.  Isopodis affines. Corpus depressum, lineare. 
Antennz pediformes. Abdomen abnormale, 5-articulatum, stylis duo- 
bus. Antennz pediformes. Pedes tertii quartique breves, sex sequen- 
tes elongati, Caprelliformes. 
In the following synopsis, the synonymy is included only so far as it is not con- 
tained in the work on Crustacea by Milne Edwards (Paris, tome iii, 1840) ; copious 
notes also are added. "The number of new genera introduced since 1840 is quite 
large, and a few are iustituted from the collections by the writer in the Exploring 
Expedition.* 
We add a word on a single point in the distinctions of genera. The size of the 
hands among the Orchestidze and Gammaridze has often been deemed to some extent 
an important generie character. But itis now well known that the gradations in 
the same group are imperceptible, and farther, females may have minute and hardly 
prehensile feet, while in males of the same species the corresponding hands are quite 
large. On this ground, Fr. Müller has lately denied the propriety of separating the 
Orchestiz, and Talitri (Archiv für Naturg., 1848, p. 53). "There is however a wide 
difference between the species having a styliform joint terminating the second pair 
of legs and those with a hand however minute or obsolescent. "The only safe course 
appears to the writer to consist in drawing the line between species having a finger 
or claw however sinall or large, closing upon the fifth joint, and those species having 
an, extended finger or claw not closing vp. Kxóyer's Anonyz, according to his descrip- 
* 'The Crustacea of the Exploring Expedition under Captain Wilkes will form a 
volume of text in 4to, accompanied with figures of all the species in a folio atlas. 
Brief descriptions will from time to time appear in the Proceedings of the American 
Academy of Arts and Sciences of Boston, a part of which, relating to the Entomostraca 
and including upwards of 150 species, has already been published. "The number of 
new species of Amphipoda in the collections exceeds eighty. 
1 
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