LOXOCONCHA— XESTOLEBERIS. 189 



This very well-marked species is a characteristic inhabitant of brackish water, being 

 seldom or never found living in purely marine situations. In the water of salt marshes, 

 estuaries, and at the heads of contracted bays where there is much influx of fresh water, 

 it often occurs in great abundance, and in such situations it appears to be generally 

 distributed round the coasts of Europe. 



Distribution. Recetit. — Great Britain and Europe. 



Fossil. — Scotland : Govan. South Wales : New Dock-basin at Cardiff. 



6. LoxocoNCHA FRAGiLis, G. 0. Sars. Plate XIV, figs. 30 — 32. 



LoxocoNCHA FRAGILIS, G. O. Sars. Overs. Norg. mar. Ostrac, p. 65. 



Carapace of the tnale oblong, subrhomboidal, somewhat higher behind than in front, 

 surrounded, except on the superior margin, by a broad laminar fillet, which is most 

 developed behind and on the posterior portion of the ventral margin ; height fully equal 

 to half the length ; anterior extremity well rounded, posterior rather broader, oblique and 

 produced above the middle into a short obtusely rounded beak ; superior margin straight, 

 inferior sinuated in the middle, seen from above, ovate, with pointed extremities. Shell 

 smooth, fragile, bearing usually a few scattered circular papillae, the marginal belt marked 

 with radiating hairlike lines. Carapace of the female, diflFering from that of the male in 

 the same way as in the foregoing species. 

 Length, -^th of an inch. 



Distribution. Recent. — Great Britain and Norway. 



Fossil. — Scotland : Cartsdyke, Paisley. 



Genus 7 — Xestoleberis, G. 0. Sars. 



Shell very smooth and polished, ornamented with small round distant papillae, much 

 lower in front than behind; in the female very tumid behind. Hinge-joint formed 

 by a dentated projecting crest of the left, which is received into an excavation of 

 the right valve. Ventral margin of both valves incurved in front of the middle. 

 Upper antennae six-jointed, the last four joints successively decreasing in length, and bear- 

 ing very short simple setae ; lower antennae short, four-jointed, flagellum of moderate 

 length. Mandibular palp four-jointed, " branchial appendage small and bearing 



