VEXERUPIS. 85 



it is possible to discover almost as many species as indi- 

 viduals. I am sorry to differ from Turton and the 

 authors of the ' British Mollusca'; but I do not believe 

 S. arctica to be a distinct species. The characters given, 

 in the same terms, by these writers, are equally applica- 

 ble to both forms. The " lunule-like excavation in front 

 of the beaks " arises from the anterior side being more 

 contracted than the other. Specimens enclosed in stone 

 are generally symmetrical, and less angular than those 

 which are free or attached by a byssus. The present 

 species differs from S. Norvegica in being oblong instead 

 of oval, not having a wide furrow in front, gaping much 

 less at the posterior end, and in being furnished with a 

 double ridge, which is often serrated in young individuals. 

 It is, besides, comparatively a dwarf. 



It would be tedious and unnecessary to particularize 

 all the synonyms. I have collated seventeen, the spe- 

 cific names of which are different, in addition to those 

 quoted above in describing the principal varieties. 



Genus III. VENERU'PIS* Lamarck. PL III. f. 4. 



Body oblong, thick : mantle bilobed : tubes united for about 

 two-thirds of their length, naked ; longer cirri pinnate : gills 

 and palps small: foot compressed, byssiferous. 



Shell eqnivalve, cancellated : ligament elongated, and sunk 

 within the dorsal margins : teeth, 3 in one valve, and 2 or 3 in 

 the other : pallial scar rather deeply sinuated. 



Although the shell described by Lamarck as the type 

 of Venerupis is Tapes pullastra var. perforans, the cha- 

 racters by which he defined the genus are sufficiently 

 comprehensive to apply also to V. Irus, which he in- 

 cluded in it. There is undoubtedly a great similarity 



* Koek-Venus ; per syncopen for Venerirupis. 



