156 



or less elongated, basal part not produced inside, rami narrow, styliform, sub- 

 equal, each with a single apical spine. 



Remarks. — This genus was established by Fabricius as early as in the 

 year 1798, to include the Oniscus oceanicus of Linne. It is chiefly characterised 

 by the form of the metasome, and the structure of the antennulse and uropoda. 

 Mr. Budde-Lund enumerates no less than 17 different species, 12 of which have 

 been examined by himself. Of these only a single species belongs to the North 

 European fauna; it will be described below. 



Ligia oeeaniea, (Lin.). 



(PL LXX.) 



Oniscus oceanicus, Linne, Syst. nat. ed. 12, 1. 2, p. 1061. 



Syn : Cymothoa oeeaniea, Fabr. 

 „ Ligia scojmlontm, Leach, 

 „ — belgica, Bosc. 



Specific Characters. — Body oval in form, scarcely more than twice as long 

 as it is broad, dorsal face moderately convex and slightly granulated. Cephalon, 

 when seen from above, semi-oval, with the front evenly rounded, and with a slight 

 transversal depression dorsally. Lateral parts of mesosome lamellarly expanded, 

 and defined from the corresponding segments by a slight groove, posterior cor- 

 ners obtusely acuminate. Metasome exceeding 1 / 4 , of the length of the body, and 

 rounded in form, with the epimeral plates of the 2 anterior segments concealed; 

 those of the 3 succeeding segments well developed, recurved. Last segment 

 rather broad, semilunar, evenly arched at the tip, lateral parts forming a similar 

 recurved expansion to those of the preceding segments. Eyes large and convex, 

 consisting of numerous densely crowded visual elements. Antennulse extremely 

 small, scarcely projecting in front, the first 2 joints of about equal length, last 

 one exceedingly minute, nodiform. Antennae rather strongly built and exceeding 

 half the length of the body, flageUum about the length of the peduncle, and 

 composed of about 12 short articulations. Legs moderately strong, spinous. 

 Opercular plates of pleopoda exhibiting a very delicate, branchial structure. Uro- 

 poda about the length of the metasome, basal part somewhat flattened, and slightly 

 produced at the end outside, rami twice the length of the basal part, and narrow 

 styliform, each terminating in a slender spine. Colour of dorsal face grey, with 

 a bluish or greenish tinge, and more or less distinctly variegated with irregular 

 lighter patches, legs minutely spotted. Length of adult female 20 mm., of male 

 up to 28 mm. 



