No. 13. ARCA. 



Ark Shell. Inhabitant a Tetliys. 



Shell bivalve, aequivalve, hinge with numerous sharp teeth alternately in- 

 serted between each other. This genus is divided into two principal families; 

 those having the margin entire, and those having the margin crenated; and 

 both families are again subdivided into two sections, the first distinguished by 

 having beaks recurved, the other inflected. The species described in the 

 Systema Naturae, amount to forty-two. 



This genus derives its name from Area Ark, Noah's Ark shell, from the 

 similitudes which most of the species bear, when the valves are closed, to a 

 boat or hull of a ship. Lister places some of these shells among the multar- 

 ticulate cockles, and the rest with muscles, under the title of Many-toothed 

 muscles. 



Argenville ranks them as a family of Heart Cockles, and D'Avila and 

 Gualtieri as a distinct genus; the first, under the title of Area, the other as 

 Concha Rhomboidal. These writers were succeeded by Linnaeus, who 

 considered these shells as a distinct genus, called Area. The principal 

 alteration in the Linnaean classification of the genus Area, proposed by late 

 writers, is, to reclaim only such shells under the title of Area, as are uniqui- 

 lateral with the beaks remote, and have the line of the hinge simple and 

 straight throughout, with numerous teeth placed parallel to each other, and 

 fitting between those on the opposite valve, admitting this as the character of 

 the Area, and it exactly corresponds with the Area Nose, and most others. 

 The little Area, Nucleus of Linnaeus, with its analogous species, is excluded. 

 To comprehend the latter, a new genus is recently established by the French 

 writers, under the name of Nuculus, or Nucula, the character of which is 

 remarkably decisive. It is described as a triangular or oblong shell, with the 

 sides unequal, the hinge consisting of an angulated or broken line, beset 

 with numerous teeth, which are transverse and parallel, and a single oblique 

 tooth placed under the beak, and out of the range of parallel teeth above 

 mentioned. The beaks also, instead of being remote, as in Area Nose, are 

 placed close together, and turn backwards. The Area Tortuosa is the rarest 

 of this genus, and is seldom to be met with. 

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