290 
BRITISH ENTOMOSTRACA. 
to the gills of a species of Diodon, or sun-fish, taken on the 
coast to the north-east of Nootka Sound. This unfortunate 
fish seems to have been in a diseased state, and had three 
other species of parasites adhering to different parts of its 
body. The one taken from the gills he describes as a 
species of Oniscus, and figures it in the atlas to ‘La 
Perouse’s Voyage/ and also in the ‘ Journal de Physique’ 
for September 1787. Plis description and figure show 
it to be a species of the genus Cecrops. It was Leach, 
however, who first established the genus in the ‘Enc. 
Brit. Supp./ i, 1816, and afterwards in the ‘Diet, de 
Sc. Nat/ xiv, 1819. He there pointed out the difference 
in the situation of the oviferous tubes; and the genus 
thus established was afterwards adopted by Lamarck, 
Latreille, Desmarest, Nordmann, Burmeister, Kroyer, 
Edwards, &c. 
Anatomy, 8fc . — The body is oval, thick, and of a light 
horny colour and substance. The cephalo- thoracic portion 
is of a square shape ; in the male two thirds the size of 
the whole body, and in the female about one third. 
The frontal margin has two projecting plates of con- 
siderable size, rounded, and separated from each other by 
a deep notch. 
The dorsal surface is marked by a rather deep furrow 
on each side, which divides this portion of the body into 
three parts, the middle of a somewhat quadrilateral shape, 
the lower side being the narrower, and the two lateral 
parts of a triangular form. The inferior angles of these 
project downwards on each side, considerably lower than 
the middle portion, and have the first free segment of the 
thorax lying between them. This portion is small, and 
quadrilateral ; but the succeeding ring is of considerable 
size, and has attached to its upper surface a lamellar plate, 
like the elytraform appendages found in Dinemoura, only 
it is single, and smaller than in that genus, of a rounded 
form, and notched at the middle of its posterior margin. 
The last segment of the thorax is very small in the 
