Lamarck's Genera of Shells. 25 



the ligament. The Unioncs live buried in the mud, in rivers, 

 with the beaks downwards, and many of them produce tolerably 

 fine pearls. Several are slightly gaping. 



This genus is subdivided into(l) shells with the cardinal tooth 

 short, thick, not crested, {en crete) and substriated, 30 species; 

 and (2) cardinal tooth short, flattened, prominent, and often 

 crested, — 18 species. 



Type. Unio sinuata*. (Mya raargaritifera ? Linn.) 



Shell ovate-oblong, compressed, sinuous, on the upper part 

 thick ; nates rather prominent ; cardinal tooth thick, lobed, 

 striated. Rivers of the European Continent. In all 48 species. 

 PI. I. Fig. 69. 



2. Hyriaf. 



Shell equivalve, obliquely triangular, auriculated ; base trun- 

 cated and straight. Hinge with two low teeth ; one, posterior 

 or cardinal, divided into numerous diverging parts, of which 

 the interior are the smallest; the other, anterior or latera., 

 very long, and lamellar. Ligament external, linear. The 

 Hyria is distinguished from the Unio, by its general form, and by 

 the cardinal tooth, particularly that on the right valve, which is 

 divided into numerous lamellar folds, the innermost very small, 

 and has the appearance of a bundle of very unequal, diverging 

 laminae. This compound tooth is rather depressed than pro- 

 minent, and always inclines towards the posterior side of the 

 shell, instead of rising perpendicularly to the plane of the valve. 



Type. Hyria avicularist. (Mya Syrmatophora ? Gmel.) 



Shell with umbones and nates smooth ; ears large, produced 

 to a point, subacute. Brazil ? 2 species. PI. I. Fio-. 70. 

 3. Anodonta§. 



Shell equivalve, inequilateral, transverse. Hino-e linear 

 without teeth. Base of the shell terminated by a smooth car- 



" Sinuous. 



t Tfior, a Aonfj^comft— alluding, we suppose, to the form of the cardinal 

 tooth. 

 t Allied to tlie avkuUt. 

 % A»»Ji/;, from a, not, and »J«t, a loolli, having no teeth. 



