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SPECIES XL Unio dilatata (Elliptic dilatata.} 



Shell elliptical, oblong, slightly attenuated 

 posteriorly, thick, almost smooth ; epidermis red- 

 dish brown ; nacre violet ; cardinal tooth obtuse, 

 thick ; lamellar tooth very slightly inclined. 

 Length i diam. f axis of the breadth. 



A handsome species, very common ; nacre 

 beautiful, often changeable purple or bluish, more 

 or less deep or pale ; breadth three to four 

 inches; epidermis varies red or brown ; muscular 

 impressions striated ; fossule apparent ; cardinal 

 tooth thick, rugose ; lamellar tooth obtuse ; ani- 

 mal vellowish. 



SPECIES XII. Unio latissima-(Elliptio latissima.) 



Shell elliptical-oblong, slightly attenuated pos- 

 teriorly, thick, smooth ; epidermis blackish ; nacre 

 flesh coloured, with a white margin ; cardinal 

 tooth obtuse, wrinkled ; lamellar tooth carinated, 

 very straight and long. Length f diam. 1 

 axis I of the breadth. 



A large species, attaining eight inches in 

 breadth ; not so common as the preceding ; car- 

 dinal tooth somewhat trihedral ; muscular im- 

 pressions smooth ; fossule slightly marked ; lamel- 

 lar tooth carinated, sharp, thick, horizontal ; 

 3* 



