ETHERIA. 



L€tmarck. —Annales du Mus, v. 10. t. 29 — 32, 



TESTA irreguiarisV inaequivalvis^ adhaerens^ um" 

 honibus brevissimis, basi testae subimmersis, 

 Cardo edentulus^ undatus^ subsinuosus^ insequalis. 

 Impressiones musculares duse^ distantes^ laterales^ 

 oblongae. Ligamentum externum^ contortum^ 

 intus partim penetrans. — Lam. 



First distinguished by Lamarck in tlie Ann&les du Museum, 

 On account of its irregular form and foliated structure it 

 might be mistaken for an O street^ but from that it may be 

 distinguished by its having ^zoa oblong muscular impressions^ 

 in which character it approaches nearer to Cliarna; its hinge, 

 however, is toothless, and has a strong, partly internal, 

 ligament. Several species are described by Lamarck, all of 

 which are found attached by the exterior of their lower 

 valve to submarine rocks, and inasmuch as they conform to 

 the irregularities of the place, cannot be strictly said to 

 have any peculiar form, the muscular impressions^ however, 

 are lateral and rather distant. The beautiful pearly lustre 

 of the substance of the shell in two species is much dwelt 

 tipon by Lamarck. 



Two circumstances observable in the specimen of Etk. 

 semilunata^ drawn in our plate, would have induced us to 

 suspect that this was a fresh water shell, or at least an 

 inhabitant of festuaries at the mouths of rivers; 1st, its 

 having an epidermis, which remains only in those parts 

 least exposed to the action of the water, the greater part, 

 particularly of the upper valve, being eroded in a very 

 irregular manner ; and 2dly, its being partly covered with 

 the remains of those ovate vesicular bodiesj supposed to 



