LOXOCONCHA. 185 



height equal to at least half the length ; anterior extremity rounded ; posterior scarcely 

 rounded, rather oblique, subangular below and sloping steeply above to the dorsal 

 margin ; superior margin arcuate ; inferior nearly straight, and forming almost a right 

 angle with the hinder extremity. Seen from above, ovate, tapering in front to an obtuse 

 point ; posterior extremity narrow and deeply emarginate, greatest width less than half 

 the length. The shell of the male is longer and narrower, with an almost flat superior 

 margin. Surface perfectly smooth, whitish, or pellucid brown. 

 Length, ^th of an inch. 



Distribution. Recent. — Great Britain, Norway. 



Fossil. — England : Tertiary, Barton. Scotland: Post-tertiary, Duntroon, Crinan. 

 Norway. 



Genus 6 — Loxoconcha, G. 0. Sars. 



Valves nearly equal, subrhomboidal, and mostly flexuous in outline, evenly convex. 

 Surface smooth or marked with concentrically arranged impressed puncta or with 

 polygonal fossae, often also with minute circular papillae. Ventral margin forming a 

 prominent compressed keel behind the middle ; postero-superior angle obliquely truncate. 

 Hinge-joint formed by two small teeth at the extremities of the hinge-line of each valve. 

 Limbs of the animal slender and colourless. Upper antennse very slender, six-jointed, 

 the last joint very long, linear, and bearing long simple setae ; lower antennae four- 

 jointed, the third joint long and narrow ; flagellum long and biarticulate. Mandibular 

 palp three-jointed, bearing a distinct branchial appendage. Lowest seta of the branchial 

 plate of the first pair of jaws deflexed. Feet long and slender, alike in male and female. 

 Abdomen terminated by a hairy conical process ; postabdominal lobes bearing two 

 moderately long subequal setae. 



The members of this genus are easily recognised by their obliquely quadrangular or 

 " peach-stone-shaped " outline. They occur in considerable abundance in our seas as 

 well as in the Glacial clays, but the number of species is comparatively small. The 

 females in this genus are very much more common than the males. 



1. Loxoconcha impress a {Baird). Plate VIII, figs. 1 — 4. 



1850. Cytheee impbessa, Baird. Brit. Entom., p. 173, pi. xxi, fig. 9. 

 1854. — v\jk\iD A, Zenker. Anatomisch. -System : Studien iiber die Krebsthiere, 



p. 86, pi V B. 



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