171 



last segment considerably produced. Eyes large, sublateral. Antennulse with the 

 terminal joint well developed. Antennae slender and elongated, with the flagellum 

 composed of 3 articulations. Mandibles with numerous penicils behind the cutting 

 part. Legs moderately slender, gradually increasing posteriorly. Opercular plates 

 of uropoda without any air-cavities, those of the 2 anterior pairs deeply bilobed. 

 Uropoda rather produced, with the inner ramus originating far in front of 

 the outer. 



Remarks. This is the genus first established, and indeed formerly em- 

 braced all the Oniscoida. In the restriction now generally adopted, it comprises 

 only a restricted number of species, chiefly characterised by the broad, depressed 

 body and the 3-articulated flagellum of the antenna?. Only a single species be- 

 longs to the fauna of Norway, and will be described below. 



Oniscus asellus, Lin. 



(PI. LXXV.) 

 Oniscus asellus, Linnaeus, Fauna suecica, IV. p. 183. 



Syn: Oniscus murarius, Cuvier. 

 /bssor, Koch? 



Specific Characters. Body rather regularly oval, greatest width exceeding 

 half the length, dorsal face but slightly convex, and, in adult specimens, nearly 

 smooth, and glossy, in younger specimens of a duller appearance, being rough owing 

 to small tubercles occurring especially on the anterior part of the body. Cephalon to 

 a great extent flanked by the side-plates of the 1st segment of mesosome, and 

 fully twice as broad as it is long, frontal edge obtusely angular in the middle, 

 lateral lobes rather prominent, narrow linguiform, dorsal face clothed with small 

 rounded tubercles. Side-plates of mesosome greatly prominent, lamellar, sub- 

 contiguous, all terminating behind in an acute corner. Metasome about half the 

 length of the mesosome and not much narrower, the 2 anterior segments very 

 small and wholly embraced by the preceding segment, epimeral plates of the 3 

 succeeding segments narrowly produced and strongly recurved, the posterior pair 

 extending almost as far as the last segment; the latter much longer than it is broad 

 at the base, outer part narrow conic, convex above. Eyes oval and but slightly 

 convex. Antennulae with the terminal joint about the length of the basal one, 

 and conically tapered. Antennae long and slender exceeding half the length of 

 the body, flagellum shorter than the last peduncular joint, and having the 1st 

 and last articulations of about equal length, the middle one shorter. Legs rather 

 slender, with the outer joints densely spinous inside. Uropoda with the outer 



