Dr Johnston’s Contributions to the British Fauna. 
the four first and the four last short* transverse, and bear- 
ing appendages; the mid one naked, had* the length of the 
body. Legs of two kinds, those attached to the anterior 
segments formed for swimming, and those to the posterior 
for creeping. Caudal segment mucronate, with two lamellae 
beneath inclosing divided stiles. 
Obs. This is a new genus, instituted for the reception of an animal, which 
cannot, I think, be referred with propriety to any genus in the arrangement 
even of Dr Leach. It is so peculiar in its characters, that there is some dif- 
ficulty in assigning it a. place in the system ; but, upon the whole, it associates, 
perhaps, best with the Asellides of Lamarck. It agrees with them in the struc- 
ture and position of its aptennae and eyes, and of the caudal segment, but in 
nothing else ; and even in the above characters not very accurately. Eut I 
am too little acquainted with the Crustacea to be able to trace its relations. 
If we are to consider, as I presume we are, those parts only as feet which 
are attached to the body (the first segment on the head, and the last on the 
tail being excluded), then the Leacia will have only twelve, three pairs formed 
for swimming, and three for creeping, placed at opposite extremities, and se- 
parated by a wide and naked interval. On the under and posterior part of the 
first segment there are, however, two pairs of organs, which resemble the 
swimming feet in every thing, except in being shorter and thicker. These 
may be considered as auxiliary maxillae, and they seem well adapted to fulfil 
the purposes of such ; but that they have the proper form and location of these 
organs, as determined by Savigny, I will not take upon me to affirm. An- 
other singularity of the Leacia is the middle segment, resembling in form the 
large shield of the lobster tribe, but peculiar in having affixed to it neither 
feet nor other appendage. 
This genus I have named in honour of Dr Leach, a naturalist who has 
contributed much to the progress of Zoology, and more particularly to our 
knowledge of that class of animals to which the Leacia belongs. 
1 . Leacia lacertosa. 
Des. Body linear, subcylindrical, one inch and a half from the tip of the 
antennae to the opposite extremity, of a dirty white colour, spotted with brown. 
Antennae four ; superior approximate at the base, on a subglobular peduncle, 
four-jointed, with a few minute hairs at the apex ; inferior, nearly as long as 
the body, crustaceous, tapering, with seven joints, of which the first is very 
short, the next twice as long, the third and fourth still longer and nearly 
equal, the three terminal short, with minute spinous hairs on the internal 
margin. Head larger than the following segment, with dilated sides, and two 
small tubercles between the eyes; below carrying two pairs of auxiliary 
maxillae? similar in structure, but shorter than the swimming legs. Eyes 
two, sessile, distant, black, reticulated. Three first segments short, trans- 
verse, with a dilated process on each side that overhangs the tubercles, from 
which the swimming feet arise. Swimming feet equal, three pairs, five-jointed, 
joints elongate, and ciliated on their internal margin with long white hairs. 
The next segment (the fifth, if the head be included) is very large, equal in 
