G'enera of Gammaracea. 137 
IV. Pedes tertii quartique subcheliformes. 
l. Antennz sup. appendieulate. Pedes tertii quar- 
tique validi, articulo quarto dilatato instar palmse, 
ungue conico, aculeato. Pontoporeia* (Króyer). 
SuBrAM. ll. GanMMaARINX. 
Antennz superiores ad basin tenues. Epimera sive grandia sive an- 
gusta. Pedes 6 postici non prehensiles. 
I. Pedes subcheliformes nulli, secundis parvulis interdum exceptis. 
1. Antennz superiores appendiculatze. Alibrotus (M. Edw.) 
2. Antenne sup. non appendiculatze. Acanthonotus (Owen). 
IL. Pedes primi subcheliformes, secundi non subcheliformes, reliqui 
non prehensiles. 
l. Àntennse sup. appendieulatze. Leptochirus] (Zaddach). 
III. Pedes primi secundique subcheliformes, reliqui non prehensiles. 
A. Antenne secunda sublus primas insita. 
* Digiti toti uni-artieulati. 
a. Pedes sex postici similes. 
1. Antenne sup. appendiculata. Gammarusi (Fabr.). 
2, Antenns sup. non appendiculatze. Amphithóe8 (Leach). 
* Tids.iv, 152. * Pedes primi et secundi paris perbreves, robusti; illi manu latá 
instructi ungue vero breviore; hi manu carentes ungueque przditi rudimentari. 
Pedes tertii quartique paris longiores, validi, subcheliformes, articulo quarto dilatato 
palmam efficiente, ungue armati conico, aculeato. Pedes quinti et sexti paris re- 
eurvi, articulo primo parum modo dilatato ungue armati perpusillo. Pedes septimi 
paris recurvi, articulo primo permagno, clypeiformi; articulo sexto vel ungue rudi- 
mentari  Epimera magna." 
4 Syn. Crust. Pruss. Prodromus, 1844. "This genus is stated to be allied to Am- 
phithoe. 
[ From the genus Gammarus, Leach separates :— 
MugRA (Edinb. Encyc., vii, 403; Trans. Linn. Soc, xi, 3859.) Manus secundee valde 
inzeque, majore bene cheliformi. 
MzrrrA (Edinb. Encyc, vii, 403.) Digitus pedum secundi paris in latus manüs 
claudens. 
The Amathia of Rathke (Fauna der Krym, Mem. Acad. Imp. St. Petersburg, iii, 
1837, p. 291, and Beit. zur Fauna Norwegens, Act. Leop. xx Bd.) includes those 
Gammari which have the superior antenne shortest—apparently an unimportant 
distinction. 
$ Amphithóe includes the Deram?ne and Pherusa of Leach.  .Eusirus of Króyer 
(Tids., N. R., i, 501,) is somewhat peculiar in the form of the hands, but the gradations 
among the species are such that the character is not sufficient even for a subgenus. 
Kroyers Microcheles (Tide, N. R., vol.ii)is also near Amphithóe. "The principal 
oint of difference mentioned is the absence of the molar prominence from the man- 
dible. The sma// hands to which the name alludes is common to many Amphithóes, 
especially females. 
The Zphimedia of Rathke (Beit. zur Fauna Norwegens, p. 85; Act. Leop., Bd. xx) 
appears to differ little from Amphithoe. The superior antenne are shorter than the 
inferior, and this characterizes generally the species from the higher latitudes. .4can- 
thosoma of Owen (Ross's 2d voyage to the north in 1829-1833, Append. p. xci) has 
the same characters. "The description of Iphimedia by Rathke is as follows—p. 89. 
* Antenne superiores inferioribus breviores; illarum peduneulus e tribus, harum e 
quatuor articulis, compositus: omnium flagellum tenue, multiartieulatum. ^ Pedes 
secundi paris manibus simplicibus, primi paris, illis minores, chelis instructi, quarum 
pollex ex uno tantum articulo constat. Reliqui pedes iis Gammarorum similes, 
Pedes spurii in duos ramos plus minusve complanatos divisi." 
