70 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
and may reach a size of 26 mm., their extreme width 
bemg 11 mm. ‘The dorsal face of the body is moderately 
convex, and its surface is granulated. he body can be con- 
veniently divided into four regions—1l, the head segment 
or cephalon; 2, the mesosome or thorax, consisting of 
seven segments; 3, the metasome or abdomen, consisting 
of five distinct abdominal segments, together with a 
terminal segment, which is, 4, the telson. 
The cephalon is sunk into a depression formed by 
the forward growth of the epimeral portions of the first 
thoracic segment. It is evenly convex in front; the 
posterior border is depressed, the edge being marked by 
a ridge. ‘The dorsal surface is slightly curved trans- 
versely. A pair of large compound sessile eyes are 
situated laterally, each having a slight reniform appear- 
ance from a dorsal view. On the anterior face, which is 
almost vertical, the minute pair of first antennae are 
situated, one on each side the median line. To the 
outside of these are the large and robust second antennae. 
When moving, the animal holds the large antennae in a 
forward position, and constantly tests the nature of the 
surface over which it is proceeding with the very sensitive 
flagella, appearing to trust for guidance more by this 
means than by means of its sight. When at rest, they are 
folded back along the sides of the mesosome. 
On the ventral side of the head the mouth-parts form 
a prominent projection. The mouth is bounded in front 
by a large transversely-hinged labrum. The sides are 
composed of the powerful mandibles and two pairs of 
maxillae. ‘The posterior border is formed by the two 
maxillipedes, which are imperfectly fused together, 
forming an apparent lower lip; there is, however, internal 
to these, a lingua-like bilobed chitinous plate, deeply 
incised in the middle and having a small median plate; 
