NEW GENUS OF AMFHIPOD CEUSTACEANS. 
635 
thoracic region. Even the claw which Phronima usually has on the fourth leg is repre- 
sented here by the enlarged terminal joint of the last pair of thoracic legs. 
The three pairs of abdominal feet and the segmentation of the abdomen present 
only very small differences from Phronima , in which there is one pair of appendages 
more than in Thaumops. 
In both forms the nerve-chain shows five ganglia in the thoracic region. In the 
abdominal region Thaumops has three ganglia for five, Phronima five for five, segments. 
Both forms alike have very large compound eyes, with an externally faceted cornea 
and crystalline bodies. The general conformation of the stomach in Thaumops is similar 
to that of Phronima , only in the former the csecal appendage is developed to an extra- 
ordinary degree. The intestinal tube presents nothing remarkable. The heart is con- 
fined, as in Phronima , to the anterior part of the thoracic region, and the gills are three 
pairs, with nearly the same form and mode of attachment in both cases. 
The genital papilla in Thaumops is in the centre of the first thoracic segment, while 
in Phronima it is in the seventh body-segment. The ovaries in Thaumops seem to be 
double, and are of a cylindrical form, while in most other known Amphipods they are 
cylindrical. 
Thaumops is nearly related to Phronima ; nevertheless I do not think it can form 
a member of the family Phronimidse, as the transformation of the first two pairs of 
thoracic appendages into maxillipeds, the absence of mandibles, the entirely different 
structure of the head, the genital papilla being situated in the first body-segment, and 
the last pair only of the thoracic appendages being enlarged and bearing claws, seem 
to me to be characters of more than generic value. 
As to the habit of life of Thaumops, the question arises whether it is a pelagic 
animal (like Phronima ) which may have been caught in the trawl on its way up from 
the depth to which it had been lowered, 1090 fathoms, or whether it lives on the 
bottom. I have already given my reasons for thinking that this Crustacean is not a 
good swimmer, and for suggesting that it may, like Nymphon, live at the bottom ; but 
I am well aware that these reasons are not sufficient to establish the point, which must 
be kept open to be decided by future observations. 
Description op the Plates. 
PLATE XLIX. 
Fig. 1. Thaumops pellucida, seen from below. nat. size. 
A. Head with the cephalic ganglion and the nerves departing from it. 
o. The mouth. 
B. Five pairs of feet attached to the thoracic region. 
, gp. Genital papilla. 
mx. Maxillipeds. 
mdccclxxiii. 4 Q 
