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. His 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, 



Anatomy, Sj'c. 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 



