76 

 Limnoria lignorum (Eathke). 



(PI. XXXI.) 

 Cymothoa lignorum, Ratlike, Skrifter af Naturh. Selsk. Vol. 101, PI. 3, fig. 14. 



Syn: Limnoria tcrebrans, Leach. 

 untinata, Heller. 



Specific Characters. Body, when fully extended, about 3 times as long as it 

 is broad, and almost semi-cylindric in form, slightly tapering in front. Cephalon 

 nearly globular, and partly covered above by the 1st segment of mesosonie, front 

 obtusely rounded. First segment of mesosome considerably longer than the others 

 and rather deep, forming below, on each side, a rounded lobe projecting over the 

 lateral faces of the cephalon. Coxal plates fringed with ciliated bristles, the 2 {in- 

 terior pairs oval quadrangular, the 4 posterior ones considerably larger, and pro- 

 duced to an acute corner pointing backwards. Metasome considerably exceeding half 

 the length of the mesosome, and scarcely narrower, epimera triangular, projecting 

 laterally; terminal segment about the length of the other 5 combined, and very 

 broad, almost elliptical in form, posterior edge evenly arcuate and finely ciliated. 

 Eyes comparatively small, rounded, with a limited number of large cornea;. Supe- 

 rior antennee somewhat stronger than the inferior, with the flagellum extremely 

 small, 3 -articulate, and carrying a dense fascicle of long sensory filaments. 

 Inferior antenna 1 with the flagellum about half the length of the peduncle, and 

 composed of 5 articulations, the 1st of which is much the largest. First pair of 

 legs somewhat larger than the next succeeding ones, but otherwise of the very 

 same structure, meral and carpal joints in most of the legs strongly tubercular 

 inside. Last pair considerably more slender than the others, and without any 

 tubercles. Dactylus in all legs distinctly bi-articulate, the 1st joint having at the 

 end inside, a bidentate unguiform spine. Uropoda with the .basal part strongly 

 tuberculated outside, and projecting between the rami to an acute projection, outer 

 ramus short, unguiform, turned outwards, inner sublinear, about the length of 

 the basal part, and terminating in a dense bunch of slender bristles. Colour 

 light greyish brown, with darker brown pigmentary ramifications. Length of adult 

 animal 5 mm. 



Remarks. This form was described by Kathke as early as in the year 

 1799 as Cymothoa lignorum. By subsequent authors, it has generally been re- 

 corded under the name given to it by Leach, viz., Limnoria terebrans. The Lim- 

 noria imcinata of Heller, from the Adriatic, is undoubtedly identical with the 

 northern species. 



Occurrence. I have found this form not infrequently in the Christiania 

 Fjord, at Drobak and Moss, boring in immerged pieces of wood. A single 



