22 



Var. 2. semi-radiata, olive with 

 rays, brown. 



SPECIES VI. Uniofragilis (Elliptic fragilis.) 



Shell elliptical, a little dilated posteriorly, very 

 thin and fragile, almost smooth ; epidermis olive ; 

 nacre bluish ; cardinal tooth smooth, compress- 

 ed ; lamellar tooth short. Length | diam. | 

 axis i of the breadth. 



Var. l.fuscata epidermis reddish brown. 



This species resembles the preceding very 

 much ; differing from it however in shape, which 

 is dilated instead of being attenuated, slightly 

 compressed ; ventricose, surface almost smooth, 

 &c. The apices not apparent ; animal yellowish; 

 breadth about two inches. These two species 

 nearly resemble the U. viridis, U.fasciata, U. 

 aurata, U. nasuta, &c. which are also fragile, 

 but may readily be distinguished by their teeth, 

 which are very different, being smooth ; lamellar 

 tooth somewhat curved, &c. 



SPECIES VII. Unio nervosa (Elliptio nervosa.} 



Shell elliptical, widest posteriorly, thin, with 

 flexuous nerve-like lines, concentric, vermicular ; 



