MALAC0Z0A. TROPIOPODA. LAMELLIBRANCHIATA. 341 



Family X.— Mactrina. P. 217, 286. 

 Genus 7. Ervilia. 



Shell suboval, equivalve, anisorneral, closed ; binge 

 with two divaricate teeth and an intervening sinus in 

 one valve, a single erect tooth in the other ; ligament 

 internal. Name from Ervum, a tare. Turton. 



1. Ervilia pellucida. Pellucid Ervilia. 



Shell ovato-elliptical, compressed, very inequilateral, 

 with both ends rounded, the umbones prominent, the 

 dorsal line concave, the hinge with two narrow divari- 

 cate teeth, the valves transparent, concentrically sulcato- 

 striate. Pellucidus, permeable to light. 



Shell ovato-elliptical, with the umbones very prominent, 

 and placed near one end ; the dorsal outline concave, double 

 the length of the ventral; both ends rounded; the hinge with 

 two divaricate slender teeth, separated by a triangular space ; 

 the valves thin, semitransparent, little convex, concentrically 

 sulcate, glossy, hyaline-white ; the inner surface highly glossed. 

 Length three-fourths of a twelfth, height a third less. 



Very similar in form to Montacuta substrata, but less con- 

 vex, and without diverging striae. Captain Brown refers it to 

 the genus Tellina ; but its generic characters seem to me 

 to be rather those of Ervilia. 



First found by me, on an Actinia, from the Bay of Aber- 

 deen, in January, 1843. 



Tellina pellucida. Brown, Illustr. PL 1 6. f. 22. 



Genus Rissoa. P. 56, 146. 

 18. Rissoa Bryerea. Bryers Rissoa. 



Shell oblongo-turrite, obtuse, thick, subpellucid, of 

 six little-convex turns, with numerous transverse costEe, 

 scarcely interrupted by the suture ; the last turn with 

 about twenty costae ; the aperture less than a-third of 

 the whole length, ovate, acute behind, with the outer 

 lip thickened. Named by Montagu after Mr. Brver. 



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